ISLAMABAD (AP) — Afghanistan's Taliban have announced the start of a spring offensive, promising to build their political base in the country while focusing military assaults on coalition and Afghan security forces.

Taliban spokesman Zabihullah Mujahid announced the launch of the offensive Friday in an email statement.

The Taliban dubbed this year's offensive "Operation Mansour," named for the Taliban leader killed last year in a U.S. drone strike.

While they may be officially announcing their spring offensive, recent attacks including one earlier this week on an army base in northern Afghanistan that killed more than 140 Afghan soldiers would seem to warn of a tough fighting season ahead.

As well as the Taliban, Afghanistan is also battling an emerging local Islamic State affiliate known as Islamic State in Khorasan.