The UN Security Council has strongly condemned North Korea's launch of a long-range rocket.
After an urgent meeting in New York, the council said it would soon adopt a new sanctions resolution in response.
Pyongyang said it fired the rocket to place a satellite in orbit but critics believe the real purpose was to test ballistic missile technology.
Sunday's launch came weeks after North Korea conducted a fourth nuclear test. Both acts violate existing sanctions.
Amid the tension, a North Korean patrol boat briefly crossed into South Korean territory near the island of Socheong early on Monday morning, according to South Korea's Defense Ministry.
The ministry said that it retreated back across the border - a boundary line Pyongyang disputes - shortly after South Korean forces fired warning shots into the water around it.
Speaking after closed-door talks, the Security Council said the launch was "a serious violation" of UN resolutions.
Japan's envoy to the UN, Motohide Yoshikawa, said existing sanctions "have not stopped North Korea from developing nuclear weapons" and must be tightened.
US ambassador Samantha Power said the UN would "come up with something tough", saying: "There can be no business as usual."
She said the UN hoped China, North Korea's ally, would "see the grave threat to regional and international peace and security, see the importance of adopting tough, unprecedented measures, breaking new ground here, exceeding the expectations of Kim Jong-un".
But Chinese ambassador Liu Jieyi took a less stern line, saying any resolution should "do the work of reducing tension, of working toward denuclearisation, of maintaining peace and stability, and of encouraging a negotiated solution".
North Korea's other main ally, Russia, also called for "a reasonable resolution" that would not lead to economic collapse in North Korea, or increased tensions.
Its UN Ambassador Vitaly Churkin said Russia ultimately wanted the resumption of the six-party talks on Korean denuclearisation, though he admitted that was unlikely as the North Koreans "have been very unreasonable".
Analysis: BBC's Nick Bryant at UN headquarters
The question once asked by a British tabloid - How Do you solve a problem like Korea? - still has not been answered. The UN Security Council has imposed four sets of sanctions since North Korea carried out its first atomic test almost 10 years ago.
They have included arms embargos, asset freezes, travel bans and restrictions on luxury goods, aimed at hitting Pyongyang's elites where it hurts - in their lavish lifestyles. But while they might have slowed the nuclear and ballistic missile programmes, they've come nowhere near halting them. The sanctions have not been rigidly enforced. Nor have they been widely applied.
Now the US is pressing at the Security Council for tough and comprehensive new sanctions, but they're being resisted by China, Pyongyang's closest ally and biggest trading partner.
Beijing, while expressing support for a new resolution, fears that tough new sanctions could topple the Pyongyang regime, destabilising the country and creating a refugee crisis on its border. Pyongyang knows it can exploit that fear.
Sunday's launch, which North Korea had said last week it would carry out, was hailed by state media as a "fascinating vapour... trailing in the clear and blue sky in spring of February on the threshold of the Day of the Shining Star".
A statement said a new Earth observation satellite, Kwangmyongsong-4, had successfully been put into orbit less than 10 minutes after lift-off from the Sohae space centre in North Phyongan province.
Hailing it as part of the country's peaceful space programme, a state TV newsreader said more launches were planned.
South Korean MPs were told by the country's spy agency later on Sunday that the launch should be treated as a ballistic missile test, as the satellite it put into orbit would be useless.
The MPs were also reportedly told North Korea had the technology for intercontinental ballistic missiles and was preparing a fifth nuclear test.
North Korea last fired a long-range rocket in 2012, putting what it claimed was a communications satellite into orbit. However, experts said that satellite appeared to spin out of control and the revolutionary songs that Pyongyang said it was broadcasting were never detected.
The payload this time was presumed to weigh 200kg (440lbs), double the size of the 2012 launch, but still much lighter than the 800-1,500kg usual for a satellite.
North Korea's rocket launches
- February 2016: Launch of rocket reportedly carrying satellite
- May 2015: North Korea announces it has successfully tested a submarine-launched missile for the first time, but scepticism is then poured on the claim
- Dec 2012: North Korea launches three-stage rocket, says it successfully put a satellite into orbit; US defence officials confirm object in orbit
- Apr 2012: Three-stage rocket explodes just after take-off, falls into sea
- Apr 2009: Three-stage rocket launched; North Korea says it was a success, US says it failed and fell into the sea
- Jul 2006: North Korea test-fires a long-range Taepodong-2 missile; US said it failed shortly after take-off