BAGHDAD, July 8 (Reuters) - Fiery Iraqi Shi'ite cleric Moqtada al-Sadr has gone back to neighbouring Iran, U.S. military sources in Baghdad said on Sunday.

Earlier this year, U.S. officials said the anti-American cleric was hiding in Iran to avoid a major security crackdown in Baghdad, although his aides say he never left Iraq.

"Our sources do show Moqtada in Iran," one U.S. military source said, declining to speculate on why Sadr had gone back.

A senior aide to Sadr denied the cleric had left Iraq.

Sadr disappeared from public view shortly before the launch of a U.S.-led offensive in Baghdad in February but re-emerged in the holy Shi'ite Iraqi city of Kufa on May 25.

Analysts had speculated Sadr had returned to reassert his authority over his Mehdi Army militia, which the U.S. military says has begun breaking into splinter groups.

The United States accuses Iran of fuelling sectarian violence with its support for Shi'ite militias such as the Mehdi Army. Tehran rejects this, accusing Washington of fomenting instability in the region.

Sadr has said nothing about where he had been while he was out of public view for months other than to describe it as a "successful disappearance".

His lower profile has coincided with a growing rift between his movement and Shi'ite Prime Minister Nuri al-Maliki.

Sadr pulled his six ministers out of Maliki's cabinet in April when the prime minister refused to set a timetable for the withdrawal of U.S. troops from Iraq.

The cleric's political bloc has boycotted parliament since an attack on a revered Shi'ite mosque last month in the city of Samarra and most recently rejected a landmark draft oil law.

Sadr led two uprisings against U.S. forces in 2004 before becoming more involved in mainstream politics.

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