Kurdish Peshmerga fighters from Iraq and moderate Syrian rebels continued to rain cannon and mortar fire on Islamic State (Isis) positions to the west of Kobani, but have been unable to reverse the militants' advance.

The Peshmerga fighters have been deployed behind Syrian Kurdish forces and are supporting them with artillery and mortar fire, reports Reuters.

An estimated 150 Iraqi Kurdish fighters joined them after crossing into the Syrian border town with arms and ammunition from Turkey last week.

The US military said it bombed Isis positions in Syria five times and in Iraq nine times on Sunday and Monday, including near Kobani.

But the Isis continued to inflict heavy losses on Kobani's defenders.

It also made significant gains in Syria where it seized two gas fields from President Bashar al-Assad's forces and invoking terror among Sunni tribes that opposed it in Iraq. As many as 36 members of a Sunni tribe had been executed in the provincial capital Anbar.

Weeks of fighting within full view of the Turkish border has tested Ankara which has been reluctant to engage along with Kurdistan Workers' Party (PKK) militants, who have fought a decades-long insurgency against the Turkish state.