The US is considering "all options" to give assistance in fighting militants from the Islamic State in Iraq and the Levant (ISIS), President Barack Obama said.

Deployment of US ground troops is however out of the question, the BBC quotes White House officials as saying.

Obama explained he did not "rule out anything" as Washington had to make sure the militants were "not getting a permanent foothold in Iraq or Syria".

ISIS insurgents seized the north and central Iraqi cities of Mosul and Tikrit (the hometown of former leader Saddam Hussein) earlier this week and are reportedly planning to continue south to Baghdad.

The extremist Sunni militants' intentions are to set up an Islamist enclave out of territories in Iraq and eastern Syria that are currently under their control.

At a UN Security Council (UNSC) meeting the organization condemned activities carried out by ISIS and voiced support for Iraq's government in its "fight against terrorism".

Around 500 000 people could have fled Mosul, with the UN reporting the humanitarian situation was "worsening by the moment".