KABUL A roadside bomb killed four service members from the NATO-led International Security Assistance Force (ISAF) in Afghanistan's volatile east on Monday, the coalition said in a statement, one of the worst attacks on foreign troops in recent weeks.
ISAF gave no other details, including the nationalities of those killed. Most of the troops serving in the volatile eastern provinces near the border with Pakistan are American, although some other members of the NATO force are stationed there.
Violence has surged across Afghanistan this month since the Afghan Taliban announced the start of its long-awaited "spring offensive."
U.S. commanders had warned of a spike in violence this month as the Taliban and other militants seek to hit back after NATO-led forces made significant gains in arresting a growing insurgency, particularly in the Taliban heartland in the south, over the past 18 months.
They have warned that significant attacks would be likely in the east, where the insurgency is much more fragmented, and in major cities.
On Saturday, a suicide bomber killed six medical students in an attack in the main military hospital in a heavily guarded area of the capital Kabul, not far from the U.S. embassy.
The next day, four Taliban suicide bombers staged a brazen assault on a police compound in the eastern Khost city, killing three police, two Afghan soldiers and a civilian.
The Afghan intelligence agency said on Monday the attack on the Kabul hospital was carried out with the help of a "rogue" soldier, the latest in a string of incidents where insurgents have infiltrated the Afghan police force and army.
An Afghan soldier who had been recruited by the Taliban two months ago gave the bomber, who was Pakistani, his identity card so he could enter the hospital, agency spokesman Lutfullah Mashal told reporters.
He said the soldier and four others had been detained since Saturday's attack.
Despite the presence of up to 150,000 foreign troops, violence across Afghanistan is at its worst since the 2001 overthrow of the Taliban government by U.S.-backed Afghan forces. There were record casualties on both sides last year.
The death of the four ISAF troops in the east on Monday brings the number of foreign troops killed in Afghanistan this year to at least 188, according to counts kept by independent monitor www.icasualties.org and Reuters.
Another homemade bomb killed four ISAF troops in the south a week ago, while a suicide bomber in an Afghan army uniform killed another five, as well as four Afghan soldiers, in the eastern city of Jalalabad on April 16.
At least 2,465 foreign troops have been killed in Afghanistan since the war began, roughly two-thirds of them from the United States.
Last year was by far the deadliest of the war for foreign troops, with at least 711 killed, and 2011 is on a similar trend. By the end of May 2010, 220 foreign troops had been killed, according to casualties.
Escalating violence across Afghanistan has raised questions that a plan by the United States to begin a gradual drawdown of troops in July may be premature despite recent gains. NATO is planning to hand over all security to Afghans by the end of 2014, a transition that is looking increasingly more difficult.
(Writing by Amie Ferris-Rotman; Editing by Paul Tait and Alex Richardson)