A senior US commander promised yesterday that US and Iraqi forces would not attack Moqtada al-Sadr's Mehdi Army if it stuck to a ceasefire, after militia members expressed fears it was being exploited to target them.

The Shi'ite cleric's decision to renew his ceasefire for a further six months on Friday was hailed by the Iraqi and US governments, which said it would help prevent a return to sectarian violence that pushed Iraq towards all-out civil war.

However, a number of Mehdi Army members fear the ceasefire will expose them to attacks from US and Iraqi security forces, which they have accused of exploiting an initial truce called last August to arrest scores of Sadrists.

"We want to emphasise that Iraqi security forces and Coalition forces are only targeting those that commit criminal and terrorist acts," Brigadier-General Mike Milano, deputy commander of US forces in Baghdad, told reporters.

"We will continue to treat those who honour the ceasefire with respect and restraint."

Analysts have cautioned US forces not to provoke the Mehdi Army, which has tens of thousands of fighters and was once described by the Pentagon as the greatest threat to Iraq's security. The militia staged two uprisings in 2004.

The US military has been aggressively pursuing what it describes as 'special groups', members of Sadr's militia who it says do not recognise the ceasefire and are trained and equipped by Iran. Tehran denies the accusations.