A suicide bomber has attacked a joint Afghan-NATO patrol in eastern Afghanistan, killing at least 20 people.

NATO says the deaths Monday include three coalition service members and their interpreter. U.S. officials identified the three NATO soldiers as American. Afghan officials say the blast also killed six Afghan police officers, including members of a quick reaction force.

The Taliban claimed responsibility for the attack.

Local officials say the bomber attacked the coalition and Afghan patrol as troops walked near a market in the city of Khost.

Afghan authorities say the attack wounded more than 60 people.

NATO strongly condemned the attack and offered condolences to victims' families.

Meanwhile, coalition and Afghan officials are investigating a gunbattle Saturday that killed two Americans and three Afghan soldiers. The two sides have given conflicting accounts of that incident, which came days after U.S.-led coalition forces eased restrictions on joint operations with their Afghan allies.

NATO initially described the gunbattle as a suspected “insider attack,” in which Afghan security forces or insurgents disguised in Afghan or coalition uniforms open fire on NATO personnel. But NATO coalition deputy commander Lieutenant General Adrian Bradshaw later said insurgent fire may have played a role in the fighting.

NATO also said the gunbattle began after a “short conversation” between Afghan security forces and coalition troops who were manning a temporary checkpoint nearby.

The Afghan Defense Ministry said the exchange of fire was the result of a “misunderstanding” between the two sides, an account that left open the possibility of an insider attack. Such attacks have escalated this year, killing at least 52 coalition personnel.

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