Reports say thousands of Iraqi soldiers backed by air cover and tanks are closing in on the city of Tikrit, north of Baghdad, which was overrun by Islamist-led rebels earlier this month.
A military spokesman said helicopter gunships conducted air strikes in the city early on June 28.
On June 26, military helicopters carrying airborne troops landed into Tikrit's university campus, sparking sporadic clashes.
Meanwhile, the United States has started flying armed drones over Baghdad.
The Pentagon said the drones are to protect U.S. troops who recently arrived in Iraq to assess the country's deteriorating security.
U.S. President Barack Obama has ruled out sending ground troops back to Iraq but has pledged to send up to 300 advisers, mostly special forces.
Over the past two weeks, Sunni militants led by the Islamic State in Iraq and the Levant (ISIL) have taken control of much of northern and western Iraq with little resistance, advancing to within an hour's drive of Baghdad.
General Martin Dempsey, the top U.S. military officer, told U.S. media on June 27 that "additional options" for potential future U.S. military actions in Iraq included going after "high-value individuals who are the leadership of ISIL."
Meanwhile, Iraq’s top Shi’ite cleric, Grand Ayatollah Ali al-Sistani, on July 27 called upon rival political blocs to agree on the next prime minister, parliament speaker, and president before the new parliament convenes on July 1.
Shi'ite Prime Minister Nuri al-Maliki has rebuffed calls for a more “inclusive” government, saying in a televised speech on June 25 that "the call to form a national-salvation government constitutes a coup against the constitution and the political process."