Iraq crisis: UN 'deplores' militants' capture of cities
The UN Security Council has condemned attacks by Islamist militants in two major Iraqi cities, Mosul and Tikrit.
It said the humanitarian situation around Mosul, where up to 500,000 people have fled, was "dire and is worsening by the moment".
Government forces have stalled the militants' advance near Samarra, a city just 110km (68 miles) north of Baghdad.
The US says it is considering further assistance to Iraq in fighting the militants, without giving details.
The Sunni Muslim insurgents, led by an al-Qaeda offshoot called the Islamic State of Iraq and the Levant (ISIS), have been consolidating positions in Tikrit, Saddam Hussein's hometown, which they took on Wednesday, after capturing Mosul, Iraq's second city.
Forces led by ISIS, which is also known as ISIL, also control a large swathe of territory in eastern Syria and western and central Iraq, in a campaign to set up a Sunni militant enclave straddling the border.
An ISIS spokesman has called on fighters to march on Baghdad and southern cities where the country's majority Shia Muslim community, which the group regards as "infidels", are concentrated.
It appears that ISIS and its allies want to avoid tangling with Iraqi Kurds in provinces bordering Nineveh province where Mosul is located, because they are a more cohesive fighting force, the BBC's Jim Muir reports from Kurdish-run Irbil.
While there appears to be a pause in the fighting for now, there are signs the militants may be preparing for an offensive from the west, where they control the city of Falluja, 69km (43 miles) from Baghdad, our correspondent adds.
According to AFP news agency's sources, the militants have pushed even further south, bypassing Samarra and seizing the town of Dhuluiya, 90km north-west of Baghdad.
In a statement, the UN Security Council said it "deplored in the strongest terms the recent events in the city of Mosul" and expressed concern for the hundreds of thousands who have since fled their homes.
Secretary General Ban Ki-moon called on "the international community to unite in showing solidarity with Iraq as it confronts this serious security challenge".
ISIS fighters swept south from Mosul to Tikrit, passing through the town of Baiji, where Iraq's largest oil refinery appears to still be in government hands.
US State Department spokeswoman Jen Psaki said on Wednesday that Washington was committed "to working with the Iraqi government and leaders across Iraq to support a unified approach against ISIL's continued aggression".
Iraq has been seeking American drones to root out the insurgents, a request that has so far been rebuffed by the Obama administration, the New York Times reports.
Iraqi Prime Minister Nouri Maliki has vowed to fight back against the insurgents and said he would punish troops who fled offering little or no resistance.
ISIS in Iraq
- The Islamic State of Iraq and the Levant (ISIS) has 3,000 to 5,000 fighters, and grew out of an al-Qaeda-linked organisation in Iraq
- ISIS has exploited the standoff between the Iraqi government and the minority Sunni Arab community, which complains that Shia PM Nouri Maliki is monopolising power
- It has already taken over Ramadi and Falluja, but taking over Mosul is a far greater feat than anything the movement has achieved so far, and will send shockwaves throughout the region
- The organisation is led by Abu Bakr al-Baghdadi - an obscure figure regarded as a battlefield commander and tactician. He was once the leader of al-Qaeda in Iraq, one of the groups that later became ISIS.
A police captain who fled from Tikrit told Reuters news agency that security forces had been duped by militants using "police and army Humvee vehicles".
When the militants reached the outskirts of Samarra, the government responded with air strikes.
The UN Security Council also "denounced the taking of hostages at the Turkish consulate" in Mosul.
Almost 50 Turks, including the head of the mission in Mosul, are being held by the militants.
Elsewhere in Mosul, militants are reportedly travelling around telling citizens they are not in danger - even the Shia residents.
One man who fled with his family told Reuters: "They told us not to be scared and that they came to liberate and free us from oppression. We are frightened because we don't know who they are."
Mr Maliki has asked Iraq's parliament to declare a state of emergency.
ISIS has been informally controlling much of Nineveh for months, and in the past week has attacked other areas of western and northern Iraq, killing scores.
The Iraqi government is struggling with a surge in sectarian violence that killed almost 800 people, including 603 civilians, in May alone.