KABUL, Afghanistan - An explosion against troops on a foot patrol in southern Afghanistan killed three service members Thursday, the U.S.-led coalition said.

It did not release any details about Wednesday's attack, including the troops' nationalities or the blast's location. But reports so far indicate they are not Canadian soldiers.

The countries with the most troops in southern Afghanistan are Canada, Britain, the United States and the Netherlands.

The past three months have been the deadliest for international troops in Afghanistan since the 2001 U.S. led invasion.

A record number of American and NATO troops are in the country -- around 65,000 -- exposing more soldiers than ever to increasingly lethal Taliban bombings and ambushes.

Southern Afghanistan is the centre of the Taliban-led insurgency. More than 3,200 people have died in violence countrywide so far this year, according to an Associated Press tally of figures provided by Afghan and western officials.