BAGHDAD: The US military has started flying armed drones over Baghdad to defend American troops and diplomats as Iraqi forces took their fight against Sunni insurgents to the strategic militant-held city of Tikrit.

Iraq's top Shia cleric urged the country's leaders to unite, after Prime Minister Nuri al-Maliki conceded political measures are needed to defeat the offensive that has killed more than 1,000 people and overrun major parts of five provinces.

In further fallout, the president of Iraq's autonomous Kurdish region said there was no going back on his ethnic group's self-rule in disputed territory, including the divided northern oil city Kirkuk, now defended against the militants by Kurdish Peshmerga fighters.

International agencies also raised alarm bells over the humanitarian consequences of the fighting, with up to 10,000 people having fled a northern Christian town in recent days and 1.2 million displaced by unrest in Iraq this year.

A senior US official said “a few” armed drones were being used over Baghdad as a precaution to safeguard Americans in the Iraqi capital if necessary.

But officials said the drones would not be used for offensive strikes against the Sunni Arab militant offensive, led by jihadists from the Islamic State of Iraq and the Levant (ISIL) but involving other groups as well.

The Pentagon acknowledged that among the manned and unmanned aircraft flying over Iraq to carry out surveillance, some were carrying bombs and missiles — without specifying if those planes were drones.

“The reason that some of those aircraft are armed is primarily for force protection reasons now that we have introduced into the country some military advisers whose objective will be to operate outside the confines of the embassy,” spokesman Rear Admiral John Kirby said.

Maliki insisted that “Baghdad is safe.“ A retired US general, James Conway, echoed those remarks, saying that “the worst is over” as militants will be unable to take Baghdad, the south or Kurdish areas.

In Tikrit, Iraqi forces have swooped into Tikrit University by helicopter, and a police major reported periodic clashes there on Friday.

A senior army officer said Iraqi forces were targeting militants in Tikrit with air strikes to protect forces at the university and prepare for an assault on the hometown of executed dictator Saddam Hussein.

University important step

Another senior officer said taking the university was an important step towards regaining control of Tikrit, which the militants seized on June 11.

The operation is the latest effort to regain the initiative after security forces wilted in the face of the initial insurgent onslaught launched on June 9.

Iraqi Kurdish leader Massud Barzani said Baghdad could no longer object to Kurdish self-rule in Kirkuk and other towns from which federal forces withdrew in the face of the militant advance.

“Now, this [issue]... is achieved,” he said, referring to a constitutional article meant to address the Kurds' decades-old ambition to incorporate the territory in their autonomous region in the north over the objections of successive governments in Baghdad.

“We have been patient for 10 years with the federal government to solve the problems of these [disputed] areas,” Barzani said.

“There were Iraqi forces in these areas, and then there was a security vacuum, and Peshmerga forces went to fill this vacuum. “Grand Ayatollah Ali al-Sistani, who is revered within the majority Shia community, meanwhile urged Iraqi leaders to unite and form a government quickly after parliament convenes Tuesday.

Arming moderate rebels

Sistani's remarks echoed those of British Foreign Secretary William Hague and US Secretary of State John Kerry, who visited Jeddah as Washington unveiled a $500 million plan to arm and train moderate Syrian Sunni rebels to help fight the ISIL-led militants.

On Thursday, Maliki, who has publicly focused on a military response to the crisis, said political measures were also necessary, ahead of the July 1 opening of the new parliament elected on April 30.

Iraq has also appealed for US air strikes against the militants, but Washington has only offered up to 300 military advisers.

Washington has stopped short of saying Maliki must go, but has left little doubt it feels he has squandered the opportunity to rebuild Iraq since US troops withdrew in 2011.

Mortar fire south of Baghdad on Friday killed at least five people, while shelling and clashes in Diyala province to the northeast killed 10 more, four of them soldiers.

Maliki's security spokesman has said hundreds of soldiers have been killed since the offensive began, while the UN puts the overall death toll at nearly 1,100.

The International Organisation for Migration warned that aid workers could not reach tens of thousands of Iraqis displaced by the violence, and called for humanitarian corridors to be established.