Iraqi government forces are continuing an offensive to retake the northern city of Tikrit from Sunni rebels.
Aircraft have struck at rebel positions and clashes have broken out in various parts of the city, witnesses and officials have said.
Troops had reportedly pulled back to the nearby town of Dijla as Saturday's initial offensive met stiff resistance.
The city of Tikrit was captured by Sunni rebels on 11 June as they swept across large parts of northern Iraq.
"The security forces are advancing from different areas", Lt-Gen Qassem Atta told journalists. "There are ongoing clashes."
Heavy fighting on Saturday between the Iraqi security forces and armed men from different factions controlling Tikrit caused many casualties on both sides, eyewitnesses and journalists told the BBC.
Fear inside Tikrit
"We cannot live here another day. The entire night we have only heard bombs bursting all around the hospital" - Marina Jose, one of 46 stranded Indian nurses at a Tikrit teaching hospital, tells BBC
Insurgents, led by the Islamic State in Iraq and the Levant (Isis), were reported to have shot down a helicopter and captured the pilot.
The witnesses said the Iraqi forces had been hampered in their bid to retake Tikrit by the large number of improvised explosive devices laid on the approaches to the city.
Iraq said on Sunday it had received the first batch of military jets ordered from Russia in order to help fight the militants.
The defence ministry said five Sukhoi aircraft would enter service in "three to four days".
Meanwhile, Israeli Prime Minister Benjamin Netanyahu called for the creation of an independent Kurdish state in response to gains made by Sunni insurgents in Iraq.
In a speech in Tel Aviv, he said the Kurds "are a nation of fighters and have proved political commitment and are worthy of independence."
Earlier this week, Iraqi Kurd leader Massoud Barzani told CNN that "the time is here for the Kurdistan people to determine their future".
Correspondents say the Kurds have long held aspirations for an independent state but they remain divided between Syria and Turkey, Iran and Iraq.
The international community, including neighbouring Turkey and the US, remain opposed to the breakup of Iraq.
Speaking to the BBC on Sunday, UK Foreign Secretary William Hague called for political unity in Iraq to help fight what he called the "mortal threat" to the state.
"Security operations will only work with strong political support from all elements in Iraq" he said.
Mr Hague's intervention will add to the pressure on Iraq's leaders to form a national unity government, correspondents say.
It follows a call from Iraq's most influential Shia cleric, Grand Ayatollah Sistani, for a new prime minister to be appointed by Tuesday - when the new parliament meets - to try to defuse the political crisis.
Prime Minister Nouri Maliki wants a third term, though observers say he is seen by many as having precipitated the current crisis through sectarian policies.
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