BAGHDAD  - The Iraqi government bolstered Baghdad’s defences on Friday as militants pushed towards the capital and President Barack Obama said he was exploring all options to save Iraq’s security forces from collapse.

Washington said US companies were evacuating hundreds of staff from a major air base north of Baghdad as the militants battled security forces just 80 kilometres from city limits.

With militants closing in on the capital, forces from Iraq’s autonomous Kurdish region took control of a swathe of territory they have sought to rule for decades against the objections of successive governments in Baghdad. Moreover, the United States has not begun talks with its traditional foe Iran on the renewed crisis in Iraq, the State Department said Friday, despite Washington and Tehran's shared interest in supporting Baghdad. "No, we are not talking to the Iranians about Iraq," spokeswoman Marie Harf told reporters in response to a question at her daily briefing.   BAGHDAD, June 13, 2014 (AFP) - Prime Minister Nuri al-Maliki said Friday Iraqi security forces have begun clearing cities of "terrorists," after militants seized swathes of territory and brought the military to the brink of collapse.

Security forces "began their work to clear all our dear cities from these terrorists," Maliki said in a statement, without giving details of where or when operations had started. Maliki travelled to the embattled city of Samarra on Friday, areas of which militants took last week and sought to advance into again on Wednesday.

Militants were gathering for another assault on Samarra, located 110 kilometres (70 miles) north of Baghdad, witnesses said. The city houses the revered Shiite Al-Askari shrine, which was bombed by militants in 2006, sparking a sectarian war between Shiites and Sunnis that killed tens of thousands. A major militant offensive, spearheaded by powerful jihadist group the Islamic State of Iraq and the Levant, has overrun all of one province and chunks of three more since Monday.

Militants were gathering Friday for a new attempt to take the city of Samarra, home to a revered shrine whose 2006 bombing sparked a sectarian war, witnesses said.

Witnesses in the Dur area, between militant-held Tikrit and Samarra, said they saw “countless” vehicles carrying gunmen south during the night.

On Friday, they were fighting pro-govt forces near Muqdadiyah, just 80 kilometres from Baghdad city limits. Kurdish security forces moved into the strategic Saadiyah and Jalawla districts of the province overnight after the army withdrew, Deputy Governor Furat al-Tamimi said.

Meanwhile, leading cleric Grand Ayatollah Ali al-Sistani urged Iraqis Friday to take up arms against extremists marching on Baghdad, as thousands volunteered to bolster the capital’s defences.

Sistani’s call to defend the country against the offensive spearheaded by the ISIL came as Obama said he was exploring all options to save Iraq’s security forces from collapse. “Our national security team is looking at all the options... I don’t rule out anything,” he said. One option is drone strikes, like those controversially deployed in Afghanistan, Pakistan and Yemen, a US official told AFP.

John Kerry called for Iraqi politicians to close ranks. “Now’s the time for Iraq’s leaders to come together and to show unity,” he said. Iranian President Hassan Rouhani pledged his govt’s full support against “terrorism”.

UN human rights spokesman Rupert Colville said on Friday that hundreds of people were killed, many of them summarily executed, after militants overran the Iraqi city of Mosul this week. “The full extent of civilian casualties is not yet known but reports received by UNAMI, the UN mission in Iraq, to this point suggest that the number of people killed in recent days may run into the hundreds and the number of wounded is said to be approaching 1,000,” he told a news briefing in Geneva.

UNAMI has its own network of contacts and had interviewed some of the 500,000 who fled Mosul, he said. A further 40,000 people were estimated to have fled from Tikrit and Samara, according to the International Organization for Migration.

China said on Friday that it was watching security developments in Iraq closely after fighters captured two more towns in a sweep south, and offered the government in Baghdad whatever help it can give.

China is the top foreign player in Iraq’s oilfields, which are the largest in the Middle East open to foreign investment, and has a natural interest in the country’s stability. “China is paying close attention to the recent security situation in Iraq and we support the Iraqi government’s efforts to maintain domestic security and stability. We hope that Iraq can return to stability, safety and normality as early as possible,” Foreign Ministry spokeswoman Hua Chunying said.