At least 4 service members from the NATO-led International Security Assistance Force (ISAF) in Afghanistan were killed in a roadside bomb attack on Monday, Reuters reported.

The alliance said in a statement that in recent week this is one of the worst attacks on foreign troops. The troops allocated in the volatile eastern provinces near the border with Pakistan are mostly American.

U.S. commanders had warned of significant attacks this month in the east, where the revolution is much more fragmented. Six medical students were killed in a suicide bomb attack on Saturday and the next day, six people were killed in a Taliban suicide bomb attack on a police compound in the eastern Khost city.

“The attack on the hospital was carried out with the help of a rogue soldier,” the Afghan intelligence agency told Reuters on Monday.

“An Afghan soldier who was recruited by the Taliban gave the bomber, who was Pakistani, his identity card so he could enter the hospital,” agency spokesman Lutfullah Mashal told reporters. The soldier and four others had been in custody after Saturday's attack, he added.

At least 188 foreign troops have been killed in Afghanistan this year after the death of the four ISAF troops on Monday, according to counts kept by independent monitor and Reuters. By the end of May 2010, 220 foreign troops had been killed, according to icasualties.

About 2,465 foreign troops have been killed since the war began in Afghanistan, two-thirds of them from the United States.