Afghanistan's Taliban vowed to ramp up assaults on coalition and Afghan security forces in a statement Friday announcing the start of their annual spring offensive.

The group said that they were changing tactics for this year's operation, naming it "Operation Mansour" after the group's late leader who was killed last year in a US drone strike.

The operation "will differ from previous ones in nature, and will be conducted with a twin-tracked political and military approach," the Taliban said.

Fighting will include a mix of conventional, guerrilla and suicide attacks targeting Afghan and foreign troops. The statement also indicated the group plans to use improvised explosive devices (IEDs) as well as "insider attacks."

"The enemy will be targeted, harassed, killed or captured until they abandon their last posts," the Taliban statement said, although the group promised to minimize civilian casualties.

Troops reeling from base attack

The spring offensive usually marks the start of the "fighting season," although the Taliban continued to battle government troops through the winter - including a devastating attack on a military base in northern Afghanistan last week.

At least 10 militants launched an attack on a base in northern Balkh province last Friday, storming it in three military vehicles. They killed most of their victims in a mosque inside the compound where army personnel were at Friday prayers.

At least 135 Afghan soldiers were killed according to official figures although the actual death toll is believed to be much higher. It is thought to be the deadliest strike by the Taliban on an Afghan military target.

The Taliban described the attack as a "prelude" to the spring offensive.

The assault led to the resignations of the Afghan defense minister and the army chief of staff, as well as fear and suspicion among security forces that the militants had help from inside.

At least 35 soldiers have been arrested over the attack so far, ranking from foot soldier to colonel.

US warns of 'tough year'

The attack also illustrated the troubles facing Afghan forces in containing the Taliban insurgency since most NATO troops left in 2014, leaving a training and advisory mission.

Afghan government troops saw soaring casualties last year, up by 35 percent with 6,800 soldiers and police killed in 2016, according to a US watchdog. Afghan children are paying an increasingly high price, a recent UN report showed.

The report said that as of March this year, 210 children had been killed -  up 17 percent from the same period last year.

Friday's spring offensive announcement also comes as US President Donald Trump's administration works on developing a new strategy for the embattled region.

US Defense Secretary James Mattis and National Security Adviser H.R. McMaster both visited Afghanistan this month, with Mattis warning of "another tough year" for the region in 2017.

Washington currently has around 8,400 troops stationed in Afghanistan as part of the NATO-led Resolute Support training mission. The United States also has a separate counterterrorism mission targeting fighters belonging to al-Qaeda and the so-called "Islamic State" (IS).

Earlier this month, the US military dropped it largest non-nuclear bomb on IS hideouts in eastern Afghanistan - but as of yet, there is no clarity on Washington's broader strategic objectives for the embattled region.

rs/rt (AFP, dpa, Reuters)