Three more NATO service members were killed in weekend attacks in Afghanistan, the military alliance said Sunday, making a total of eight killed on the deadliest day for foreign troops this year.

The three deaths announced Sunday came from two separate bomb attacks in the south the day prior — the same day that five NATO service members were killed in a suicide bombing by a Taliban sleeper agent at the Afghan army's eastern headquarters.

Not since last June, when 10 foreign soldiers were killed on each of two days, have so many NATO soldiers been slain in one day.

The latest attacks used improvised explosive devices, or IEDs, according to the International Security Assistance Force, as the NATO mission is known.

ISAF has not stated the nationalities of those killed in any of Saturday's incidents, which it usually leaves to its member countries.

Canada has about 2,900 troops in Afghanistan, mainly in the south. The United States has more than 100,000, largely in the south and east.

NATO officials have said they expect a particularly violent spring and summer in Afghanistan as insurgents try to pour back into areas taken over by international troops over the winter.

Fighting usually increases in Afghanistan as the weather warms and insurgents climb back over the mountainous border with Pakistan. This year, NATO has pushed further into Taliban strongholds in the south and has said their goal is to hold these areas so that militants cannot re-establish themselves.

Taliban say they had sleeper agent

Saturday's first attack, at the Afghan army base in the eastern province of Laghman, also killed four Afghan soldiers and an interpreter. The Taliban claimed responsibility for the bombing and spokesman Zabiullah Mujahid said Sunday that the soldier was a sleeper agent who had been in the army for years and had been in contact with Taliban operatives for "a long time." He said the soldier had only been at that specific base for one month.

Previously, the Taliban had said the soldier had only joined the army a month ago.

Attacks by insurgents donning security uniforms are a relatively rare but recurrent problem as NATO and Afghan forces work more closely together. Afghanistan's security forces are also ramping up recruitment of Afghan soldiers and policemen so they can take the lead in securing their nation by the end of 2014, adding more than 70,000 police and soldiers last year in an effort to reach 305,000 troopers by the end of this year.

The latest deaths make 23 NATO service members killed so far this month in Afghanistan and 125 killed so far this year. With files from CBC News