BAGHDAD (AFP) — US Secretary of State Condoleezza Rice in a surprise visit to Baghdad on Sunday said Iraqi leaders were more united than ever, as Shiite cleric Moqtada al-Sadr warned of a war against the government.

Rice also said that security in Iraq had improved, but during her stay in Baghdad’s Green Zone the heavily fortified area was rocked by an explosion which, according to a US official, could have been a rocket attack.

At least 19 people were also killed in clashes and mortar attacks in east Baghdad on Sunday.

“I see a coalescing of a centre in Iraqi politics in which the Sunnis, the Kurdish leadership and the elements of the Shiite leadership that are not associated with these ‘Special Groups’ (alleged Iranian-backed Shiite groups) have been working better than at any time before,” she said.

“It is indeed a moment of opportunity in Iraq thanks to the decision of the Iraqi prime minister and the unified Iraqi leadership.”

The US military claims that “Special Groups”, many of them from Sadr’s feared Mahdi Army militia, are being trained by Iranian covert agents to fight American forces in Iraq.

Rice stopped in Baghdad before heading to Bahrain and then on to Kuwait for talks on a regional conference of Iraq’s neighbours on Tuesday on the battered country’s security.

Her visit comes a day after Sadr threatened to declare “open war” if the crackdown by Iraqi and US forces against his loyalists is not halted.

Rice gave a cautious response to Sadr’s latest salvo which came as Iraqi and US forces battle Shiite militiamen, mostly from his Mahdi Army militia, in Baghdad’s Sadr City and in the southern city of Basra.

“It’s been very difficult to get a read of what his motivations are and what his intentions are,” Rice said.

“I know he’s living in Iran. I guess it’s all-out war for everybody but him. His followers can go to their deaths and he will still be living in Iran. I don’t know how seriously to take him or not.”

The US military threatened to strike back if Sadr wages war.

“If Sadr and Jaish al-Mahdi (Mahdi Army) become very aggressive, we’ve got enough combat power to take the fight to the enemy,” said Major General Rick Lynch, commander of US forces in central Iraq.

Iraqi and US officials said that at least 19 people were killed in Baghdad on Sunday.

US military spokesman Lieutenant Colonel Steven Stover confirmed the deaths of 12 people killed in fierce clashes in Sadr City early on Sunday.

Stover said gunmen attacked a US checkpoint with machine guns, rocket-propelled grenades and mortars around 8 am (0500 GMT). Troops returned fire killing seven militants.

They later shot dead two Iraqi snipers firing at them from a nearby rooftop, Stover said. Three other “criminals” were killed while trying to plant roadside bombs elsewhere in Sadr City, he said.

“Iranian-supported Special Group criminals are turning the streets of Baghdad into a battleground,” he added.

Later Sunday, medical officials in Sadr City said five people were killed and 15 wounded, including a three-year-old child and a woman, in renewed clashes between Mahdi Army militiamen and US-Iraqi forces.

Two people were also killed in mortar attacks in Kadhimiyah, another Shiite district of Baghdad.

Rice, who is visiting Iraq for the second time this year, said Prime Minister Nuri al-Maliki was “looking to unite all Iraqis” despite his stand-off with Sadr.

Speaking on the flight from Washington to Baghdad, Rice called on Iraq’s Arab neighbours to do more by opening full diplomatic ties with Baghdad to counter the Iranian influence.

“The neighbours could do more to live up to their obligations because I do believe the Iraqis are beginning to live up to theirs,” Rice told reporters on her plane.

Since the US-led invasion of 2003, Iraq’s Arab neighbours have worried not only about violence there but also about backing a government tilted towards Shiite Iran.

Rice urged Arabs to take special encouragement from Maliki’s decision to crack down on Iranian-backed Shiite militias, even though it has produced a spike in violence.

“At some point Arab states need to take yes for an answer in terms of… Iraq’s commitment to its Arab identity,” Rice said.

Later on Sunday, the secretary of state travelled outside the Green Zone in an armoured motorcade for talks with Iraqi President Jalal Talabani in which she said she would “engage” Iraq’s neighbours to do more to help Baghdad.

At Talabani’s palace, the walls shook following an undetermined explosion, an AFP reporter travelling with Rice said.