US forces attacked in Afghanistan

A convoy carrying US and Afghan forces was struck by a roadside bomb and came under small arms fire in Afghanistan's Nangarhar province on Monday.

The convoy returned fire in self-defense and there were no US casualties, according to a NATO press release.

But Monday's attack comes just days after three US soldiers were killed and another wounded during a joint US-Afghan military operation in the same region.

An American official said the soldiers were shot in an apparent insider attack, also known as a "green-on-blue" incident because of the color-coding system used by NATO. During such assaults, members of the Afghan security forces are known to target US and other NATO soldiers.

Taliban spokesman Zabiullah Mujahid said the militants claimed responsibility for the attack.

Both attacks occurred in the Achin District, where US and Afghan troops have been carrying out an offensive against a local affiliate of ISIS, officials said.

There are about 8,400 US troops in Afghanistan. The US counterterrorism mission is separate from the NATO-led effort to train, advise and assist the Afghan army and police force in the fight against the Taliban.

US and coalition casualties in Afghanistan have become rarer in recent years, falling dramatically since the Afghan government assumed responsibility for combat operations in 2014.

But in late April, two US service members were killed and another wounded while conducting a joint raid in the Achin District, a Pentagon spokesman said. The operation was targeting ISIS-K, the terror group's Afghanistan affiliate.

Achin District is the primary base of operations for ISIS in Afghanistan and has been the site of multiple joint US-Afghan counterterrorism missions. A US Army Special Forces soldier was killed fighting the terror group there in early April.

The district is also where the US dropped its most powerful non-nuclear bomb, killing close to 100 ISIS fighters, according to Afghan officials.

In May, military officials told lawmakers that they were considering sending additional troops to Afghanistan in an effort to "move beyond the stalemate."

The troops, which could consist of special forces personnel and more conventional soldiers, would be part of the NATO-led mission to train, advise and assist the Afghan army and police force in its fight against the Taliban but would also aid the US counterterrorism effort there as well.