US warns North Korea against provocation after execution
The US has urged Pyongyang to avoid any provocative acts following the execution by North Korea of a once-powerful political figure.
North Korea announced on Thursday that it had executed Chang Song-thaek, the uncle of leader Kim Jong-un, for "acts of treachery".
The move has raised concerns of instability in the secretive and repressive nuclear-armed country.
The US said it was consulting its regional allies.
State Department spokeswoman Marie Harf said she would not speculate on what might be happening within the North Korea regime, but that the execution of Mr Chang had been "an incredibly brutal act" which "underscores the horrific human rights record of the North Korean regime".
"We're going to increase our discussions with our allies and partners in the region about the internal situation in North Korea," Ms Harf told reporters in Washington.
"North Korea has a choice between continuing down the path of isolation and impoverishment of its own people or meeting its obligations and coming back to the international system," said Ms Harf.
She said the US "would urge the North Koreans not to take provocative acts" as it was "not in the interest of regional stability".
International talks aimed at convincing the North to denuclearise and reduce its threatening posturing towards the international community in exchange for aid have repeatedly failed.
'Worse than a dog'
Mr Chang was married to the sister of late leader Kim Jong-il, and is believed to have mentored Kim Jong-un when he succeeded his father in North Korea in 2011.
He had been seen as the second-most important figure in the country, holding several key posts, but this week was dramatically removed from a special party session by armed guards and stripped of all his titles.
On Thursday, the state news agency KCNA said he had admitted at a military trial to trying to overthrow the state, and had been executed immediately.
A long and detailed statement described him as "despicable human scum... worse than a dog".
Two of his closest aides had already been executed, and many of his subordinates and allies have reportedly been recalled to Pyongyang.
Correspondents say the speed and and brutality of Mr Chang's case has been startling. Political purges are common, but the regime rarely makes such an exhibition of senior figures who fall from grace.
However, analysts say the purge is bound to raise regional tensions.
South Korean President Park Geun-Hye has warned the North is "engaged in a reign of terror" aimed at consolidating Kim Jong-un's grip on power. The South's military has said it is on heightened alert.
South Korean Unification Minister Ryoo Kihl-jae warned the purge could be followed by military moves from Pyongyang - including another nuclear test. Military action is often used by the North as a way of curbing internal agitation.
In February it carried out its third nuclear test, to widespread international condemnation, and threatened attacks on Japanese, South Korean and US military targets in the region.
Japan said it was "closely watching" the latest situation, and would remain in communication with its neighbours on the matter, Kyodo news agency quoted Chief Cabinet Secretary Yoshihide Suga as saying.
China - Pyongyang's only ally and major trading partner - described Mr Chang's execution as an "internal matter".
"As a neighbouring country, we hope for North Korea to maintain stability..." a foreign ministry spokesman said.
Mr Chang made a high-profile trip to China in 2012 where he met then-President Hu Jintao, and signed a raft of economic deals, including the development of two special economic zones.
The BBC's Lucy Williamson in Seoul says one theory for Mr Chang's downfall is that he was too keen an admirer of China's economic reform.
The speed of his downfall has sent a powerful message to those who had hoped for change under North Korea's new leadership that he can crush any opponents, says our correspondent.
But many will be asking whether it is his nephew's hand alone behind this execution, or whether the army is seeking to reassert its power, she adds.
Kim Jong-il (d)×
Kim Jong-il was one of the most secretive leaders in the world.Tales from dissidents and past aides created an image of an irrational, power-hungry man who allowed his people to starve while he enjoyed dancing girls and cognac.
But a different picture was painted by Sung Hae-rim, the sister of one of his former partners in her memoir, The Wisteria House.
She describes a devoted father and a sensitive, charismatic individual, although she admits even those closest to him were fearful of him.
North Korean media depicted him as a national hero, whose birth to the country's founder, Kim Il-sung, was marked by a double rainbow and a bright star.
The youngest sister of the late Kim Jong-il and the wife of the man formerly regarded as the second most powerful figure in North Korea, Chang Song-thaek.
She has held a wide range of important Workers' Party positions including being a member of the all-powerful Central Committee.
Her promotion to four-star general made Kim Kyung-hee the first North Korean woman ever to achieve such status.
Analysts say Kim Kyung-hee and her husband were seen as mentors for the new leader Kim Jong-un when he came to power in 2011. But news of her husband's execution in December 2013 suggests the most significant upheaval in North Korea's leadership since Mr Kim succeeded his father.
Chang Song-thaek (d)×
Chang Song-thaek was married to Kim Kyung-hee, the younger sister of the late Kim Jong-il. When the inexperienced Kim Jong-un became the new leader in 2011, the couple were widely thought to be acting as his mentors.
In December 2013, the powerful uncle - who sat on the country's top military body - was denounced by the state-run news agency for corruption. Images were shown of him being removed from a Politburo meeting by uniformed guards. He was then executed.
Mr Chang's execution is the biggest upheaval in North Korea's leadership since Mr Kim succeeded his father.
Kim Jong-nam, 39, is Kim Jong-il's eldest son.
Sung Hae-rang, the sister of Kim Jong-nam's deceased mother Sung Hae-rim, has written in her memoir that Kim Jong-il was extremely fond of Kim Jong-nam and was pained to be away from him. Like his half-brothers, Kim Jong-nam studied at an international school in Switzerland.
His chances of succession appeared to be ruined when, in 2001, Japanese officials caught him trying to sneak into Japan using a false passport. He told officials that he was planning to visit Tokyo Disneyland.
Some analysts argued that he may have been forgiven by his father, as there is precedent for the regime reinstating disgraced figures after a period of atonement. Confucian tradition also favours the oldest son.
But in a rare interview while on a trip to China last year, Kim Jong-nam said he had "no interest" in succeeding his father.
Kim Sul-song, 36, is Kim Jong-il's daughter born to his first wife, Kim Young-sook.
Reports say she has worked in the country's propaganda department, with responsibility for literary affairs.
One South Korean report said she had also served as her father's secretary.
Kim Jong-chul, 29, studied at an international school in Switzerland. He works in the WKP propaganda department.
His mother, Ko Yong-hui, is said to have been the North Korean leader's favourite consort.
However, Kenji Fujimoto, the pseudonym of a Japanese sushi chef who spent 13 years cooking for Kim Jong-il, has written that the leader considered his second son "no good because he is like a little girl".
Kim Jong-un, the second son of Kim Jong-il and his late wife Ko Yong-hui, was anointed "the great successor" by Pyongyang.
Like his older brothers, he is thought to have been educated abroad.
A Japanese sushi chef who worked for Kim Jong-il for 13 years up to 2001 said that he "resembled his father in every way, including his physical frame".
Speculation that he was being groomed to succeed his father had been rife for years.
Since taking power, he has presided over a long-range missile test, North Korea's third nuclear test and most recently the execution of his uncle, Chang Song-thaek.
Ri Sol-ju was introduced as Kim Jong-un's wife in state media reports about the opening of an amusement park in July 2012.
Reports simply said he attended the event with his wife, "Comrade Ri Sol-ju".
Little more is known about Ri Sol-Ju, although there has been much speculation about her background since pictures first emerged of Kim Jong-un with an unidentified woman. There is a North Korean singer of the same name, but she is not now thought to be the same person.
State media did not mention when the couple got married.
The grandson of Kim Jong-il and nephew of leader Kim Jong-un has said he wants to "make things better" for the people of his country.
Kim Han-sol, 17, spoke of his dreams of reunification of the two Koreas in an television interview in Bosnia, where he is studying. Kim Han-sol said he had never met his grandfather or uncle.
He described an isolated childhood spent mostly in Macau and China, after his birth in Pyongyang in 1995. In the future, he said he pictured himself going to university and then ''volunteering somewhere''.