BAGHDAD — Radical Shiite cleric Moqtada al-Sadr on Tuesday lashed out at US Defence Secretary Leon Panetta's disclosure that American forces are keeping up unilateral attacks on Iran-backed insurgents in Iraq.

Sadr's spokesman Salah al-Obeidi charged in the Shiite holy city of Najaf, south of Baghdad, that Panetta had "openly mocked Iraq's sovereignty and flaunted security agreements" signed by Washington and Baghdad in November 2008.

"We are shocked by the lack of reaction from Iraqi political and military leaders," he said.

Panetta on Monday said US forces were pursuing Iran-backed insurgents in Iraq, as US deaths spike almost 12 months after Washington announced a formal end to combat operations in the country.

"We have to unilaterally be able to go after those threats. We're doing that," Panetta said.

"We are very concerned about Iran and weapons they're providing to extremists here in Iraq. We lost a heck of a lot of Americans as a result. We can't allow this to continue," he told troops at US Camp Victory near Baghdad airport.

Three US soldiers have been killed in Iraq so far this month, the last on Sunday when Panetta arrived unannounced in Baghdad. June was the deadliest month for US forces in Iraq since 2008, with 14 soldiers killed.

Panetta, who took over on July 1 from Robert Gates, said he would take all steps needed for the safety of the 46,000 US troops still in Iraq, down from a high of 170,000 since the 2003 US-led invasion that toppled Saddam Hussein.

The resumption of attacks against US troops comes as Iraqi leaders approach decision time on whether they want to maintain a contingent of soldiers after 2011 when all US troops are scheduled to pull out.

Major General Jeffrey Buchanan, spokesman for US forces in Iraq, last month identified the Iran-backed groups as Ketaeb Hezbollah, Asaib Ahel al-Haq and the Promised Day Brigade.

The latter is directly linked to Sadr, who divides his time between Iran and the shrine city of Najaf.

The two other groups are offshoots of Sadr's now-disbanded Mahdi Army, which fought against Iraqi and US-led coalition forces between 2004 and 2007, and which has been identified by the Pentagon as the main threat to stability.

Colin Kahl, a Panetta adviser, told reporters that US forces retained the right to carry out combat operations in Iraq. "We have self-defence authorities under the security agreement (with Iraq) to take on our own measures," he said.

US forces formally declared an end to combat missions last August.

Sadr last week withdrew a threat to reactivate the powerful Mahdi Army but said the elite Promised Day Brigade would oppose American forces if they extended their deployment in Iraq.

Panetta on Tuesday wound up a three-day visit to Iraq with a visit to the city of Arbil for talks with Massud Barzani, president of the autonomous Kurdish region of northern Iraq.

Some Kurdish officials have said they want US forces to stay beyond the end of 2011 deadline, in sharp contrast to Sadr.