Sunni militants have seized another town in Iraq’s western Anbar province – the fourth in two days.
Fighters of the Islamic State in Iraq and the Levant (Isis) captured Rutba, 90 miles (150km) east of Jordan’s border, officials said.
They earlier seized a border crossing to Syria and two towns in western Iraq as they advance towards Baghdad.
The insurgents intend to capture the whole of the predominantly Sunni Anbar province, a spokesman told the BBC.
Iraq’s government said on Sunday it had killed 40 militants in an air strike on the militant-held northern town of Tikrit, although witnesses said civilians died when a petrol station was hit.
US Secretary of State John Kerry, speaking in Cairo, said Isis’ “ideology of violence and repression is a threat not only to Iraq but to the entire region”.
Calling it a “critical moment”, he urged Iraq’s leaders “to rise above sectarian motivations and form a government that is united in its determination to meet the needs and speak to the demands of all of their people”.
Earlier, Iran’s supreme leader Ayatollah Ali Khamenei condemned the prospect of US intervention in Iraq, saying Washington’s main intention was to keep Iraq within its own sphere of power.
Dismissing talk of sectarianism, he said: “The main dispute in Iraq is between those who want Iraq to join the US camp and those who seek an independent Iraq.”
Analysis from BBC Persian’s Bozorgmehr Sharafedin
The Obama administration is signalling that it wants a new government in Iraq without Prime Minister Nouri Maliki before launching any attack on Isis, but Iran’s Supreme Leader has rejected both ideas.
Ayatollah Khamenei strongly opposed “the intervention of the US and others in the domestic affairs of Iraq”, and said the US is not pleased with the results of the new election and “is seeking an Iraq under its hegemony and ruled by its stooges”.
Khamenei’s anti-US remarks weaken the possibility of co-operation. Iran feels it has the upper hand in Iraq and would try to resolve the crisis by the help of “Iraqi people, government and Shia clerics”.
Rutba is strategically placed on the main road between Baghdad and Jordan.
It is the fourth town in what is Iraq’s largest province to fall in two days to the Sunni rebel alliance, which Isis spearheads.
On Saturday the militants said they had taken the towns of Rawa and Anah, along the Euphrates river.
And Iraqi officials admitted Isis fighters had also seized a border crossing near the town of Qaim, killing 30 troops after a day-long battle.
According to the rebels, army garrisons, including at the area’s command centre, abandoned their bases and weapons, and fled.
An Iraqi military spokesman described the withdrawal from Rawa, Anah and Qaim as a “tactical move… for the purpose of redeployment”.