(CNN) -- A roadside bomb killed four U.S. Marines in Afghanistan Saturday, the U.S. military said.
It is the deadliest single attack against American troops this year in Afghanistan, according to military figures compiled by CNN.
Another service member was seriously wounded in the attack, which happened during a combat operation in the Farah province of southwestern Afghanistan, the military said.
The Marines, from the 2nd Battalion, 7th Regiment, are part of Combined Joint Task Force Phoenix that has the mission to train and mentor the Afghan National Army and Afghan National Police.
The attack comes during an eruption of violence in southern Afghanistan.
Hundreds of Taliban fighters captured over the past six years escaped to freedom late Friday after militants attacked the main prison in Afghanistan's Kandahar province where they were being held, provincial authorities said.
Around 100 militants attacked coalition troops in Uruzgan province in southern Afghanistan early Friday, a strike that one U.S. general called the largest militant attack this year against troops. Fighting in that same region of Uruzgan also left 17 militants dead Thursday night.
There have been other recent coalition deaths in Afghanistan -- two British troops killed on Thursday in Helmand province and a Romanian soldier killed on Friday in Zabul province.