Iraqi forces were massing north of Baghdad, aiming to strike back at Sunni rebels who have taken control of large parts of the country.
The governor of Saladin province, Abdullah al-Jibouri, said 50,000 soldiers were now stationed around Samarra, intending to regain territory lost to rebel groups led by the Islamic State of Iraq and the Levant (ISIL).
Al-Jibouri, whose provincial capital, Tikrit, was taken by anti-government fighters last week, was seen on television on Friday speaking to Iraqi soldiers, the Reuters news agency reported.
"Today we are coming in the direction of Tikrit, Sharqat and Nineveh," said al-Jibouri, a Sunni ally of Iraq's Shia Prime Minister Nouri al-Maliki.
Samarra, which is 100kms north of Baghdad, has become the frontline in the battle with Sunni fighters allied to ISIL.
After rapid gains last week the rebel advance has been largely halted, with heavy fighting continuing in several towns.
Al Jazeera's Imran Khan, reporting from Baghdad, said Iraqi forces were in control of the oil refinery outside the town of Baiji, 43km from Tikrit.
Map: ISIL's path through Iraq
Tribal leaders had negotiated a rebel withdrawal to the town, which they control completely, Khan said.
Pressure on Maliki
The rapid gains by the rebels prompted the United States to on Thursday announce the deployment of 300 military advisers to Iraq, stopping short of granting Maliki's request for air strikes.
US President Barack Obama called on the Iraqi prime minister to do more to overcome sectarian divisions that have fuelled resentment among the large Sunni minority.
The US president stopped short of calling for Nouri al-Maliki to resign as Iraqi prime minister, saying it was not up to the US to choose Iraq's leaders.
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Obama's comments were echoed by the French Foreign Minister Laurent Fabius who said Iraq needed a national unity government "with or without" Maliki.
Fabius said it was critical for the Iraqi government to reach out to ordinary Sunnis before they sided with ISIL.
Iraq's Shia-led government has been accused of pursuing anti-Sunni policies, pushing some Sunnis towards supporting ISIL.
The al-Qaeda splinter group, which has its roots in the war that followed the 2003 US invasion of Iraq, is known for its fiery rhetoric, and targeting of Shias.
Pictures published by ISIL-related Twitter accounts last week showed dozens of Shia Iraqi soldiers being executed by the group.