* Second attack on pilgrims on same road in three months

* Iran blames U.S. forces in Iraq

(Adds Iran comment, updates death toll, adds byline)

By Suadad al-Salhy

BAGHDAD, July 22 (Reuters) - At least five Iranians were killed on Wednesday when gunmen opened fire on a convoy of buses of religious pilgrims visiting Shi'ite Muslim holy sites in Iraq, police in Diyala province said.

The attack took place on a highway connecting the Iranian border to Baghdad and southern Iraq, 45 km (27 miles) northeast of the provincial capital Baquba, a police official said.

He said five pilgrims were killed, including one woman, and 35 others were wounded. Iranian media said six people were killed and 31 wounded.

A doctor at a hospital in nearby Khanaqin said four of the dead were women.

He said survivors told him that gunmen on motorcycles blocked the road as the convoy was making its way back to Iran, stopping the last bus and opening fire. Interior Ministry forces have been protecting such convoys on the highway, where at least 57 people, mostly Iranian pilgrims, died in an attack in April inside a roadside restaurant where the group had stopped.

That attack, which took place amid a spate of bombings against Shi'ite targets, raised fears that Iraq might slide back into the worst of the sectarian war that has killed tens of thousands since the U.S.-led invasion in 2003.

In Iran, a state broadcasting website reported that Foreign Ministry spokesman Hassan Qashqavi condemned Wednesday's attack as a "terrorist act" and "against divine and human values".

"The outcome of (U.S.) occupation is still providing grounds for terrorists to continue their criminal acts," Qashqavi was quoted as saying.

The statement echoed condemnation of the April attack on Iranian pilgrims, in which Iran's Supreme Leader Ayatollah Ali Khamenei pointed a finger at U.S. forces in Iraq.

The United States has long accused Iran of meddling in Iraq by funding and arming Shi'ite militiamen, while Iran blames the over six-year U.S. presence for inciting chaos and bloodshed.

Security has improved greatly in Iraq, but the future is by no means assured as Iraq's untested security forces take over from U.S. soldiers in many areas and insurgents demonstrate their resilience in ethnically mixed areas like Diyala.

Pilgrims from Iran have flocked to Iraq by the millions since the fall of Sunni Arab Saddam Hussein. Religious tourism is a boon for Iraqi cities like Najaf and Kerbala, home to Shi'ite holy sites. (Additional reporting by Tehran bureau, writing by Missy Ryan; Editing by Diana Abdallah)

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