Two coalition soldiers were killed in separate incidents in Afghanistan on Thursday, ISAF said, with the Ministry of Defence in London confirming one of them was British.
The ministry said the British soldier was killed when an improvised explosive device was triggered in Sangin in the troubled southern Helmand province while he was on patrol.
The International Security Assistance Force said that the other soldier was killed and four were wounded in southern Afghanistan "during an attack from insurgents."
"It is ISAF policy to not release the nationality of any casualty prior to the relevant national authority doing so," it said.
The latest deaths took to 193 the number of international soldiers killed in Afghanistan this year.
On Wednesday, three Canadian soldiers were killed and five wounded in an insurgent attack on their armoured vehicle in southern Kandahar province.
There are about 70,000 international troops in Afghanistan, most of them deployed under NATO to help Kabul fight a Taliban-led insurgency.
A total of 117 British soldiers have now died in Afghanistan since the late 2001 US-led invasion of the country to oust the Islamist Taliban from power.
"It is with deep regret that the Ministry of Defence must confirm that a soldier from 1st Battalion The Royal Irish Regiment has been killed," the MoD said in a statement.
"Early this morning whilst conducting a routine foot patrol near Sangin District Centre, a soldier was involved in an explosion which is believed to be caused by an improvised explosive device.
"Despite the best medical efforts at the scene, the soldier died as a result of his wounds."
Lieutenant Colonel David Reynolds, spokesman for British Forces in Afghanistan, said: "This is a tragic loss and one that will be felt across the Task Force.
"Our thoughts and sympathies are with the friends and family at this most difficult time."
Britain has approximately 7,800 soldiers based in Afghanistan, a number soon set to rise to 8,000, most of whom are stationed in Helmand.
