Islamic State militants have been steadily losing ground in Iraq since last the summer, but it is still too early to say the Iraqi government and the U.S.-led coalition are winning the fight, a military official said.

Pentagon officials released a map Monday showing Islamic State militants have lost about 25 percent to 30 percent of the territory they held at their peak of power in last August when President Obama first authorized airstrikes.

"ISIL is being slowly pushed back," said Army Col. Steve Warren, a Pentagon spokesman, using an alternative acronym for the militant group.

"The combination of coalition air power and Iraqi ground forces are having an effect on the enemy's ability to hold territory and have freedom of movement," Warren said.

However, he added: "It's still early. This is a long fight, so I am not prepared to say that the tide of battle has turned."

Iraqi Prime Minister Haider al-Abadi will visit Washington this week, meeting with Obama on Tuesday. Abadi reportedly will ask for additional U.S. weapons, such as drones, Apache attack helicopters and fresh stocks of ammunition, to help fight the IS militants.

Last summer the militants, with support from many local Sunni tribal leaders, seized most of Iraq's territory in which Sunni Muslims are a majority. Iraqi army units collapsed or fled in droves, leaving behind large stocks of American-made weaponry that were seized by Islamic State fighters.

Since then, U.S. aircraft have launched thousands of airstrikes on IS targets in Iraq and the the group has lost about 5,000 to 6,000 square miles of populated territory, Warren said.

The militants have lost ground both to Iraqi government forces as well as the Kurdish peshmerga forces in northern Iraq. That includes parts of Irbil, Babil, Kirkuk, and Diyala, Nineveh and Saladin provinces, Warren said.

"Essentially, the front line, if you will, has been pushed either west or south," he said.

But many key battles remain. The strategically important city of Tikrit is still contested after more than a month of Iraqi army operations aimed at ousting the militants.

"We haven't finished completely clearing Tikrit, but I think Tikrit will be cleared relatively soon," Warren said.

The nearby oil refinery and town of Bayji remain contested after months of intense fighting on the ground and airstrikes from U.S. and coalition aircraft.

Large parts of Anbar province in western Iraq also remain under Islamic State control, according to the map released by the Defense Department.