U.S. and Afghan officials say an Afghan soldier has shot dead an American service member in southern Kandahar province.

The incident late Wednesday is the latest in a series of attacks on international troops by their Afghan counterparts.

NATO did not give any other details but said the man who started shooting was killed when coalition forces returned fire. A joint Afghan and coalition team is investigating the incident.

In the east Thursday, NATO said three coalition service members were killed in a bomb blast. A NATO statement provided no other details but the Associated Press cited a U.S. official as saying that all three were Americans.

In other violence, a mortar fired during fighting between NATO troops and insurgents hit a house in central Wardak province, killing three women and wounding at least four others.

And in northern Badakhshan province bordering Pakistan, Tajikistan and China, a group of Taliban insurgents ambushed a police post late Wednesday, killing at least four police officers and capturing 16 others.

According to the U.S. Defense Department, at least 80 NATO troops have been killed by Afghan security forces since May of 2007. U.S. officials say many of the so-called “insider attacks” are motivated by personal issues.

International combat troops are in the process of withdrawing from Afghanistan and transferring full security responsibility of the country to Afghan forces by a 2014 deadline.