"Iranian forces hit a border area called Haj Omran and then entered 5km (3 miles) into Iraqi territory and hit the area of Lollan with heavy artillery with 180 shells targeting PKK positions," an Iraqi defense ministry statement said.
The shelling was the second attack on the Kurdish guerrillas by Iranian forces in 10 days. The previous attack on April 20 killed two guerrillas dead and wounded 10.
The Kurdish rebel group, Kurdistan Workers' Party (PKK), which has dug in in Iraq's northern Kurdish-controlled area on the border with Iran and Turkey, have warned Iran not to interfere in its fight against Turkish rule in the southeast of the country.
For around a year, Iran has been battling border infiltrations by a group called Pejak, which Tehran says is linked to the PKK.
Recently, Turkey had deployed more than 30,000 additional troops in the southeast along its rugged border with Iraq and Iran to fight the Kurdish guerrillas and to stop them from coming across the frontier.
The move came after Kurdish rebels reportedly killed two Turkish soldiers and wounded a third in a grenade attack on a military outpost, raising the number of Turkish troops killed this year to 17. More than 40 Kurdish guerrillas have been killed in the same period in a series of clashes.
The Turkish deployment, which has been going on for several weeks, boosts a large garrison in the region that by some estimates tops 250,000 soldiers.
Iran has also reportedly moved forces to its border with Iraq near the mountainous region near Haj Omran.
Jalal Talabani, the Iraqi president, who is Kurdish, has expressed concern over reported Iranian and Turkish troop concentrations on the borders.
PKK guerrillas have bases in northern Iraq, but they also have substantial forces in the mountains of southeastern Turkey. They typically step up their attacks in the spring, when winter snow melts, clearing mountain passes in the region.
Turkey often increases its military activities in response.