World Bulletin/News Desk

Iranian Supreme Leader Ayatollah Ali Khamenei blamed Western powers on Tuesday for the rise of ISIL (IS) insurgents in Iraq and Syria and said they had no business tampering with the region's geopolitics.

Iran and the United States have been arch-foes for decades but now share a strategic interest in reversing the territorial gains of IS that threaten to remake the Middle East map.

But cooperation has been blocked in part by the fact Tehran and Washington back opposing sides in Syria's civil war, where ISIL is among rebel forces fighting President Bashar al-Assad. While Washington opposes Assad, it sees IS as a bigger threat and is staging air strikes to try to neutralise the al Qaeda offshoot with the support of Western and Gulf Arab allies.

"(The) current imbroglio is the outcome of irresponsible acts in Syria by alien powers along with certain regional countries," Khamenei said, according to a statement read on state television, an allusion to mainly Turkey and Saudi Arabia.

He praised Iraq for "refusing to allow its soil to be used" against Assad, which Tehran has shored up against rebels bent on toppling him with the support of Western and Gulf Arab foes.

"We must firmly withstand them," Khamenei said, referring to those arrayed against Assad. "(I have) no faith in the sincerity of the (U.S.-led) coalition against ISIL. We believe the problem of ISIL and terrorism should be tackled by regional countries."

Last month, Khamenei said he had personally rejected an offer from the United States for talks to fight ISIL.

Khamenei spoke on Tuesday while receiving new Iraqi Prime Minister Haider al-Abadi at his residence.

Khamenei promised to "spare no effort to uphold Iraq's security and territorial integrity ... The complex situation of the region makes security of its countries inseparable. Security of brotherly, neighbourly Iraq is as indispensable as our own."

Separately on Tuesday, Iranian President Hassan Rouhani was quoted by state media as assuring Abadi in a meeting that Tehran "will continue to support Baghdad by providing military advisers and weapons to the government".

Rouhani also called for greater regional cooperation to fight ISIL. "Terrorism and extremism should be confronted in a united and coordinated way ... This is the only way to uproot this phenomenon," Rouhani said.

Iran, which fought a war with Iraq in the 1980s when it was under the rule of Sunni dictator Saddam Hussein, has since June been sending weapons to Kurdish forces in northern Iraq and military advisers to help the Iraqi army against ISIL.