The Iraqi military has launched an operation to drive Islamic State (IS) militants out of Tikrit, the hometown of former dictator Saddam Hussein.
Security officials said they plan to attack the city from the west and south, but had been slowed by land mines, roadside bombs, and snipers.
Tikrit, which is 140 kilometers from Baghdad, was taken by the IS in June. Iraqi forces failed to recapture the city last month.
Iraqi and Kurdish forces have been encouraged by U.S. air strikes launched earlier this month against the extremist Sunni insurgents, who control large parts of northern and western Iraq and swaths of Syria.
U.S. President Barack Obama said on August 18 that the retaking of the Mosul dam by Iraqi and Kurdish Peshmerga forces was a "major step forward" in battling the militants.
He said that if the dam on the Tigris River had been breached, it could have had catastrophic consequences and endangered American Embassy personnel in Baghdad.
Obama added that the United States' interests lay in seeing that a "savage group" like IS is contained, because "ultimately" it could threaten the country.
That’s why, he said, the United States has embarked on a long-term mission to defeat IS fighters in Iraq.
He said the United States is urgently providing arms and assistance to Iraqi security forces as well as Peshmerga fighters.
In addition to the Mosul dam, the Peshmerga also recaptured several towns and villages nearby.
The Mosul dam is the largest in Iraq and considered a key part of the country's infrastructure.
Meanwhile, the UN refugee agency says it is launching a major aid operation to get supplies to more than half a million people -- mostly Yazidi and Christian religious minorities -- who have fled their homes since the IS's latest offensive earlier this month in northern Iraq.
A four-day airlift of tents and other goods will begin on August 20 to the main Iraqi Kurdish city of Irbil and will be followed by road convoys from Turkey and Jordan.
UN High Commissioner for Human Rights spokesman Adrian Edwards called the operation a "very, very significant aid push and certainly one of the largest I can recall."
The militant group's advances in northern Iraq have prompted the United States to launch air strikes in the country for the first time since its military withdrew in 2011.
The U.S. Central Command said in a statement that U.S. warplanes and drones carried out 15 air strikes on August 18 near the dam.
The statement said that, since August 8, a total of 68 airstrikes have been conducted in Iraq -- 35 of them in support of Iraqi forces fighting near the dam.
In related news, the Islamic militant group has reportedly warned the United States it will attack Americans "in any place" if the raids hit its militants.
The Reuters news agency reported that a video, which shows a photograph of an American who was beheaded during the U.S. occupation of Iraq, featured a statement which said in English, "We will drown all of you in blood."