Four US soldiers fighting with the Nato-led alliance were killed in a suspected "insider" attack in southern Afghanistan today, a spokesman for the coalition said.
One of the six members of the Afghan National Police operating the observation post with six coalition troops was also found dead, while the other five had disappeared.
The attack in southern Zabul province, came a day after two British soldiers were shot dead by a man wearing an Afghan police uniform while returning from a patrol in southern Helmand province, one of the strongholds of the Taliban-led insurgency.
It brings the total number of deaths this weekend caused by Afghans turning on their allies to six
At least 51 foreign military personnel have been killed in "insider" attacks this year, deaths which have put a heavy strain on trust between the coalition and Afghanistan as they move towards handing security responsibility to Afghan forces by the end of 2014.
The rise in such attacks has led to the training of new recruits to the Afghan army and police being suspended.
The Nato-led coalition and its Afghan counterparts have created a special Joint Casualties Assessment Team to investigate every attack.
Adding to the toll of coalition deaths caused by insider attacks over the weekend, two soldiers were killed and nine wounded in an attack on Camp Bastion on Friday.
It was one of the worst attacks on a Nato-operated base all year.
Prince Harry was at Camp Bastion at the time of Friday's attack, but was unharmed.
Six Harrier jets were destroyed and two were significantly damaged in the raid on the camp airfield, carried out by 15 insurgents wearing US Army uniforms, the Nato-led coalition said in a separate statement on Sunday.
Operating in three teams, they succeeded in breaching the perimeter of the heavily fortified base.
Meanwhile, a soldier from The Queen's Company, 1st Battalion Grenadier Guards who was killed in Afghanistan on Friday was today named by the Ministry of Defence as Lance Corporal Duane Groom.
ITV News' Deputy Political Editor Chris Ship on a weekend of severe setbacks for the coalition mission.
In another development, it has emerged that Nato-led air strikes in southern Laghman on Saturday killed eight women, according to a local official.
The coalition acknowledged up to eight civilians could have died as a result of the bombing, but said a "large number" of insurgents had been killed in the strike.
Villagers said the death toll was higher and expressed outrage at being unable to pick up the bodies because the area had been closed off.
Relations between the Nato-led coalition and its Afghan partners have also been strained by civilian casualties.
Despite efforts to limit such deaths, over 200 civilians have been killed by foreign troops this year so far, according to figures provided by the coalition, around 50 percent fewer than a year ago.