Baghdad, Iraq ? The Iranian military seized five Iraqi soldiers after a cross-border skirmish between the two forces, Iraqi authorities said Friday.

The captured troops were part of a joint American-Iraqi patrol that trekked on Thursday afternoon to a border post near Mandali, a town of 13,000 located 90 miles southeast of Baghdad, to investigate reports that a large number of Iranians were crossing into Iraq there, according to Brig. Gen. Subhi Bairam, commander of the Mandali police.

Iranian forces opened fire when the patrol moved within about 50 yards of the border, Bairam said. The patrol returned fire and then retreated from the scene. Back at Mandali, they realized that five soldiers and their vehicle had been captured by the Iranians.

The Iranian military said it arrested the troops for “infiltrating the Iranian soil,” according to the official Islamic Republic News Agency. Iran also said it had arrested seven soldiers, not five.

The announcement of their capture came as sectarian violence continued to roil the country.

Three Shiite Muslim pilgrims were killed and two were wounded by mortars in Musayyib, south of Baghdad, as they marched to a major religious celebration in the holy city of Karbala, according to Capt. Muthana Ahmad of the Babil province police. More than a million pilgrims are expected to gather in Karbala today for the Shabaniya, which commemorates the birth of one of Shiite Islam’s most revered religious figures.

In Baghdad, bombs killed four people and wounded five in separate attacks on police patrols in the eastern part of the city, said Brig. Gen. Abdul Kareem Muhammad of the Interior Ministry. At least 11 other people were killed in other attacks around the country, police said.

The U.S. military also announced that an American soldier was killed early Friday morning when his vehicle was struck by a roadside bomb south of Baghdad. No other details were released.