An Afghan soldier killed one U.S. marine and wounded another before being shot to death in return fire Sunday in southern Afghanistan, the latest in a series of attacks against foreigners blamed on government forces within their own ranks.

Nearly 20 such attacks this year have raised the level of mistrust between the U.S.-led coalition and their Afghan partners as NATO gears up to hand over security to local forces ahead of a 2014 deadline for the withdrawal of combat troops.

The Afghan soldier opened fire on international troops in the Tarekh Naver in the Marjah district, a former Taliban stronghold that was the site of a major offensive by coalition forces in 2010, said a spokesman for the governor of Helmand province.

Consulate plan on block

The United States is considering abandoning plans for a consulate in northern Afghanistan because the building chosen was deemed too dangerous to occupy. The U.S. spent $80 million on the project despite glaring security deficiencies in the former hotel, according to a copy of a document drafted by the U.S. Embassy in Kabul.

Those problems — including shoddy construction that would lead to a "catastrophic failure" of the building in a car bomb attack — were overlooked and waivers to strict State Department building rules were granted as officials rushed to open the consulate in Mazar-i-Sharif as a sign of America's long-term commitment to Afghanistan, the diplomatic memo shows.

U.S. Embassy spokesman Gavin Sundwall declined to comment on the report, saying only that "the security situation has evolved in Afghanistan and any decisions we make are driven by our responsibility to ensure the safety of our personnel."

A senior U.S. defence official in Washington said Sunday the victim was a U.S. marine in Helmand province, and that one other marine had been wounded. The official, who spoke on condition of anonymity because the attack is under investigation, had no other details.

The shooting marks the second recent killing of a U.S. marine in Helmand by an Afghan soldier. Lance Cpl. Edward Dycus was shot in the head by an Afghan soldier in Helmand's Marja district while on guard duty on Jan. 31 and died the next day.

The insider threat to foreigners trying to mentor Afghan security forces has existed for years but has grown more deadly.

The U.S.-led coalition routinely reports each time an American or other foreign soldier is killed by an Afghan in uniform, but the military is underreporting the number of overall attacks. The Associated Press reported earlier this month that the coalition does not report attacks in which the Afghan wounds or misses his U.S. or allied target. It also doesn't report the wounding of troops who were attacked alongside those who were killed.

Attacks on the rise

The number of such attacks have been on the rise. So far this year there have been 19 attacks killing 12 soldiers, compared with 21 last year killing 35 coalition service members, according to NATO figures. That compares with 11 fatal attacks and 20 deaths the previous year. In 2007 and 2008 there were a combined total of four attacks and four deaths.

U.S. officials say that in most cases the Afghans who turn their guns on their allies are motivated not by sympathy for the Taliban or on orders from insurgents, but rather act as a result of personal grievances against the coalition.

Also Sunday, a NATO service member was killed by a bomb in eastern Afghanistan, the alliance said, raising to 139 the number of foreign troops deaths so far this year.