KABUL (Reuters) - Seven members of the NATO-led International Security Assistance Force (ISAF) were killed by a roadside bomb in southern Afghanistan on Thursday, the coalition said, the worst single incident involving foreign troops in a month.
The ISAF did not specify the nationalities of those killed but U.S., British and Canadian troops make up the bulk of the foreign force in the south.
Almost 200 foreign troops have been killed in Afghanistan so far this year.
Another ISAF service member was killed earlier on Thursday when a helicopter crashed in the east of the country, the coalition said. The cause of the crash was under investigation.
The coalition usually does not disclose the nationalities of those killed until the defense ministries of the countries concerned have been informed.
Homemade bombs -- or "improvised explosive devices" -- are weapons used frequently by insurgents in Afghanistan and account for more than half of the casualties suffered by foreign troops.
"Seven International Security Assistance Force service members died following an improvised explosive device attack in southern Afghanistan today," ISAF said in a brief statement.
The toll from Thursday's attack was the worst among foreign troops from a single incident since eight U.S. service personnel and a U.S. contractor were shot dead by an Afghan air force pilot at a military airport in Kabul on April 27.
Casualties among foreign forces have risen in recent weeks since the Taliban began a long-expected "spring offensive."
U.S. commanders had already said a surge in violence could be expected as Taliban-led insurgents pushed back after mainly U.S. forces made a concerted drive in the Taliban heartland in the south in the past year.
Foreign troops are preparing to start a gradual reduction in forces from July, with the last foreign combat troops due to leave Afghanistan by the end of 2014.
At least 38 foreign service personnel have been killed so far this month, according to tallies kept by independent monitor www.icasualties.org and Reuters. Fifty-one were killed in April, the worst month so far this year.
Civilian and military casualties reached record levels in 2010, the worst year of the war since U.S.-backed Afghan forces toppled the Taliban in 2001.
A total of 711 foreign troops were killed last year and 2011 is following a similar pattern, with casualty tolls rising during the spring and summer. At least 198 foreign troops have been killed this year.
Of roughly 2,480 foreign troops killed in Afghanistan since 2001, more than 1,580 were American.
(Reporting by Paul Tait; Editing by Andrew Dobbie)