U.S.-led forces backed by warplanes battled militants in southwestern Afghanistan, killing 28 rebels including several Taliban commanders, an Afghan official said Monday.

NATO said it killed several more insurgents in coordination with Pakistani forces along the mountainous border, while three troops from the U.S.-led coalition died when their vehicle rolled into a riverbed.

The accident happened Sunday when the troops were patrolling in Arghandab, a valley in Kandahar province that foreign and government forces recently retook from Taliban militants, the coalition said. It released no other details.

Fighting between insurgents and security forces is escalating, dampening the prospects of the Western-backed effort to stabilize the country succeeding any time soon. The violence has killed more than 2,000 people so far this year, according to an Associated Press tally.

In the bloodiest of the latest incidents, the U.S.-led coalition said its troops came under fire Sunday in the Khash Rod district of Nimroz province as they searched compounds for a Taliban leader suspected of involvement in suicide attacks.

The troops killed "multiple militant groups" with small-arms fire, and airstrikes killed two more groups of attackers, the coalition said. There were no coalition casualties, it said.

While the coalition said only that "several" militants died and another was detained, Nimroz Gov. Ghulam Dastagir Azad said 28 rebels were killed. He said some of the victims were torn apart in the late-night bombing, making the body count difficult.

Azad said local officials had told him that four civilians also died.

His account could not be independently verified.

The governor said the slain militants included three Taliban commanders, each of whom controlled a group of some 40-50 fighters. He said they were suspected of targeting road construction crews with bombs and planning attacks on food relief convoys.

NATO said the border skirmish happened Monday in Khost province.

Insurgents inside Afghanistan fired rockets and guns at an alliance outpost in Spera district, a NATO statement said. The troops responded with mortar and artillery fire and called in warplanes.

When the militants crossed into Pakistan, the troops "coordinated" with their Pakistani counterparts. "The Pakistan border force fired artillery on the retreating insurgents inside Pakistan," it said.

Elsewhere, the Afghan Defense Ministry said it lost two soldiers to a roadside bomb in Zurmat district of Paktia province on Monday. Two militants were killed in a clash with Afghan soldiers in Helmand province, it said.

In Logar province, just south of the capital, officials said militants attacked the government office in the town of Azra Monday, killing one civilian employee and wounding three police.