US Marines of the 1st Battalion 7th Marines Regiment arrive for a shura meeting between US Marines, local police and residents at PB Fulod in Sangin on June 12, 2012. (ADEK BERRY/AFP/GettyImages)
By Erin McLaughlin, ABC News
Four American service members were killed by an Afghan policeman early today, the third attack on coalition forces in three days, bringing the death toll in the recent violence to eight.
The attacks -- two "green on blue" incidents and an assault on a coalition base by 15 Taliban fighters -- come as tensions flared across the Muslim world over an anti-Islam film that was produced in the United States.
In the latest attack, an Afghan police officer turned his gun on NATO troops at a remote checkpoint in southern Afghanistan before dawn. Four U.S. soldiers were killed before the shooter escaped, bringing the total of coalition troops killed to six in just two days.
International Security Assistance Force officials say the attacker is still at large, and noted it's unclear if there were multiple assailants. It is still unclear exactly what transpired at the checkpoint, according to Afghan officials, who say American forces responded to an attack on the checkpoint to help the Afghan police.
"The checkpoint was attacked last night. Then the police started fighting with the Americans," Ghulam Gilani, deputy police chief of Zabul province, said. "Whether they attacked the Americans willingly, we don't know."
A Taliban spokesman said the police involved were not affiliated with the Taliban insurgency.
Also today, NATO confirmed that an airstrike that killed as many as 45 insurgents also killed five to eight Afghan civilian casualties -- including women and children.
"ISAF takes full responsibility for this tragedy," the coalition said in a statement released after the strike.
The civilian casualties can only increase tensions in the country, and villagers who drove the bodies of the dead to the privincial capital, Mehterlam chanted "Death to America," Laghman provincial government spokesman Sarhadi Zewak said.
"Protecting Afghan lives is the cornerstone of our mission and it saddens us when we learn that our action might have unintentionally harmed civilians," said Jamie Graybeal, a spokesman for international military in Afghanistan.
So far this year, 51 coalition troops have been killed by Afghan service members. At least 12 such attacks happened in August alone, leaving 15 dead.
News of the shooting comes after one of the biggest attacks ever on an ISAF base. On Friday, 15 Taliban attackers, dressed in U.S. Army uniforms, attacked Camp Bastion in Afghan's Helmand province.
According to the ISAF, the insurgents used automatic rifles, rocket-propelled grenades and explosive suicide vests in the late night attack. Two U.S. Marines were killed, and nine others were wounded, including one civilian contractor.
During the attack, which officials say appeared to be well planned and rehearsed, the insurgents destroyed six Harrier fighter jets, worth about $20 million each, and damaged two others. They also damaged six hangars and destroyed three refueling stations.
The last attack in which so many U.S. aircraft were destroyed at one time is believed to have been more than 40 years ago, during the Vietnam War.
All but one of the insurgents were killed by return gunfire, and a 15th was captured. The Taliban claimed responsibility for the attack, saying it was revenge for the controversial video made in the United States that insults the Prophet Muhammad.
Prince Harry, a member of the U.K. military in Afghanistan is based at Camp Bastion. When he was first stationed there, the Taliban said they were out to kill him, although NATO officials say he was several miles away, and was never in danger during this attack.
On Saturday, two British troops were killed in an attack in Helmand province carried out by a gunman in the uniform of a government-backed militia.
Recent months have seen a string of attacks by Afghan forces against their international counterparts, who are working towards handing over security responsibilities to the Afghans as international troops draw down.
This weekend's attacks come amid turmoil throughout the Middle East, where anti-American protests have flared up, ostensibly in response to the online video mocking the Prophet Muhammad.
An attack on the American embassy in Libya last week led to four deaths, including the American ambassador to Libya. The protests have prompted the removal of U.S. personnel from their posts in Sudan and Tunisia.
U.S. Ambassador to the UN Susan Rice told Jake Tapper on "This Week" the attack was not premeditated, contradicting top Libyan officials who say the attack was planned in advance.
Defense Secretary Leon Panetta says the turmoil raging across the Muslim world will likely continue for days, but the violence appears to be leveling off.
He said the Pentagon has "deployed our forces to a number of areas in the region to be prepared to respond to any requests that we receive to be able to protect our personnel and our American property."
ABC News' Muhammad Lila and The Associated Press contributed to this report.