U.S.-led coalition forces called in airstrikes against the Taliban, killing a dozen militants during fighting in southern Afghanistan that has displaced many families, officials said Tuesday.

Meanwhile, an old mortar round exploded in the north of the country, wounding 17 children.

The coalition said in a statement that its troops opened fire and called in airstrikes Monday after observing militants trying to set up an ambush. The coalition had been targeting a Taliban commander transporting weapons.

The troops also discovered weapons and ammunition in a search of compounds in the area, it said.

Fighting has intensified in the southern province of Helmand since U.S. Marines pushed into the town of Garmser late last month aiming to cut Taliban supply lines in the heart of the insurgency.

About 1,200 families — an estimated 7,000 people — have left their homes in recent weeks because of the fighting in Garmser, said Mohammad Nader Farhad, spokesman for the U.N. High Commissioner for Refugees.

About 900 of those families have relocated to Lashkar Gah, the capital of Helmand, and about 300 have moved to neighboring Kandahar province, Farhad said. They families were staying with relatives and friends or in rented houses.

Farhad said the government is assessing the situation, and UNHCR, along with other U.N. agencies, is prepared to assist the families as needed after the findings are complete.

Helmand Gov. Ghulab Mangal denied there had been a major exodus, but said authorities would compensate all families whose homes were damaged or destroyed during the fighting.

Mangal said about 150 militants, including foreign fighters from Pakistan, Uzbekistan and Chechnya, have been killed since the operation began. He said there are still about 500 insurgents in and around Garmser.

A U.S. military spokesman could not immediately be reached to comment on the governor's claim.

In the northern town of Baghlan on Tuesday, a boy dropped an old mortar shell that he was trying to exchange for ice cream with a scrap metal dealer, said police officer Habib Rehman.

The shell exploded, wounding 17 children and a man. Fourteen of the children were evacuated to a hospital in Baghlan. Three others were sent to the nearby town of Pul-e-Khumri, said Dr. Narmgui from the Baghlan hospital. Like many Afghans, Narmgui goes by one name.

Afghanistan is littered with old ordnance left over from decades of war.

On Monday, a rocket hit a house in the eastern Kunar province, wounding two children and a man, said provincial deputy police chief Abdul Sabor Allayer. He blamed insurgents for the attack.

At least 1,200 people — mostly militants — have died in insurgency-related violence in 2008, according to a tally compiled by The Associated Press of figures from Western and Afghan officials.

The U.N. says insurgency-related violence killed more than 8,000 people last year.