Iraq's prime minister has asked the United States to carry out drone and air strikes against Islamic State of Iraq and the Levant (ISIL) fighters, but the US has so far refused to get involved, according to a report.

The New York Times reported on Wednesday that the request was made by Nuri al-Maliki last month as the threat from ISIL escalated.

Al Jazeera's David Schuster, reporting from New York, said while there had been no official comment from the US on the story, US officials had been "quick to point out that the situation in Iraq is under constant review".

"The response could be quite different in the days and weeks ahead," Schuster said.

Sources in Washington indicated that the US was weighing possibilities for more military assistance - including drone strikes - to Baghdad. However, others signalled that the US instead wanted to strengthen Iraqi forces.

The city of Tikrit on Wednesday became the second to fall to ISIL in two days.

Sources told Al Jazeera that gunmen had set up checkpoints around the city, which lies between the capital Baghdad and Mosul, Iraq's second largest city which was captured by ISIL on Tuesday.

"All of Tikrit is in the hands of the militants," a police colonel told the AFP news agency. A police brigadier general told AFP that fighters attacked from the north, west and south of the city, and that they were from ISIL.

A police major told the agency that ISIL had freed about 300 inmates from a prison in the city, which is the capital of Salaheddin province.

UN condemnation

Iraqi state television reported that special forces soldiers were fighting to regain control of city. Sources claimed the Iraqi soldiers had cleared the city of ISIL fighters, but these reports remain unverified.

Profile: Islamic State in Iraq and the Levant

There were reports that the nearby city of Kirkuk, home to Iraq's biggest oil refinery, was also being attacked by ISIL. Fighters had guaranteed the safety of Iraqi soldiers if they gave up their weapons.

The AFP reported overnight that ISIL had advanced in the Hawijah, Zab, Riyadh and Abbasi areas west of Kirkuk.

It was also reported that 15 Iraqi security personnel had been executed at their posts.

Maliki has been meeting Iraqi politicians and Kurdish regional leaders to reach an agreement on declaring a state of emergency throughout the country.

A parliamentary vote on declaring a state of emergency could not go ahead because the session was unable to reach quorum.

Al Jazeera's Imran Khan, reporting from Baghdad, said privately some Iraqi officials were afraid Maliki was taking advantage of the situation to consolidate his position and accused him of a "power grab".

The fighting comes after half a million people are reported to have fled Mosul since the city fell to ISIL.

The Geneva-based International Organisation for Migration said the Mosul takeover had "displaced over 500,000 people in and around the city", a quarter of the city's population.

The Turkish government also said that ISIL had stormed its consulate in Mosul, taking staff and the consul captive.

The UN Security Council on Wednesday condemned the upsurge of violence and the taking of Mosul by what it described as a "terrorist organisation" attempting to destabilise the region.

The 15-nation council also demanded the immediate release of the Turkish hostages.