Why Iran rejects U.S. action in Iraq as militants push east

Fighters of the Islamic State of Iraq and the Levant (ISIL)
 stand guard at a checkpoint in the northern Iraq city of Mosul

(Reuters) - Iran's supreme leader accused the United States on Sunday of trying to retake control of Iraq by exploiting sectarian rivalries, as Sunni insurgents drove toward Baghdad from new strongholds along the Syrian border.

Ayatollah Ali Khamenei's condemnation of U.S. action in Iraq came three days after President Barack Obama offered to send 300 military advisers in response to pleas from Iraq's government. It ran counter to speculation that old enemies Washington and Tehran might cooperate to defend their mutual ally in Baghdad after two weeks of swift territorial gains by Sunni Islamists.

On Sunday, militants overran a second frontier post on the Syrian border as the Islamic State of Iraq and the Levant (ISIL) pursues the goal of its own caliphate straddling both countries.