The Taliban said Wednesday their spring offensive in Afghanistan will begin this week, the first time the insurgents' annual campaign against the Afghan government will take place without NATO troops on the battlefield.

In past years, spring and the melting of snow on the mountains along the border with Pakistan marked a significant upsurge in the fighting between the Taliban and NATO forces along with their local allies. This fighting season, the insurgents will face just Afghan forces after the withdrawal of most international combat troops at the end of last year.

A Taliban statement, which was emailed to media, said the offensive _ dubbed ``Azm'' or perseverance in Dari and Arabic _ will begin on Friday. It added that the Islamic Emirate of Afghanistan, as the Taliban call themselves, is ``determined to prolong the ongoing jihad,'' or holy war.

The statement also said that under U.S. leadership, the ``crusaders'' will maintain ``control of our land and space'' through security agreements with the Afghan government. The agreements allow NATO and the U.S. to keep a limited number of non-combat troops in Afghanistan to train and assist Afghan forces in their fight against the insurgency.

``For the complete liberation of our beloved homeland from the yoke of foreign occupation and for the implementation of Islamic rule throughout the country, the Islamic Emirate is determined to prolong the ongoing jihad against the foreign invaders as well as their internal stooges,'' the Taliban said.

In recent weeks, attacks in the north and east of the country have intensified in the build-up to the warm weather fighting season. The insurgents can be expected to fight until snow falls on the Hindu Kush, when the militants return to the mountains. Fighting even stops in many places for meals and prayers.

But after more than a decade of war, the Taliban appear no closer to their goal of overthrowing the Kabul government.

This has opened up an opportunity for what is perceived to be an affiliate of the Islamic State group, which already controls large parts of Iraq and Syria, to establish a small presence in Afghanistan. The development has alarmed many Afghans, including influential warlord Ismail Khan, former governor of western Herat province, who called on President Ashraf Ghani to improve security and kickstart a moribund economy to avoid a war with an IS offshoot.

Afghan forces have been fighting local Taliban in southern Helmand province for more than two months now, hoping to dislodge them from one of their bastions ahead of the spring offensive. Fighting has been fierce as the insurgents seek to protect supply lines for men, guns and drugs that provide a major source of their funding. Helmand's opium crop accounts for most of the world's heroin supply.

Despite the nascent IS presence, the Taliban also appear to be spreading their own influence to areas where they have not had a significant presence in the past. In northern Samangan province, police said that a firefight broke out late on Tuesday when they surrounded a house where Taliban fighters were holding a meeting.

Sediq Azizi, spokesman for the provincial governor, said Afghan security forces killed a Taliban commander identified as Mullah Bashir along with four other insurgents. One policeman was killed, he said, and another two were wounded. Bashir's mother was also wounded, he said.

In eastern Nagharhar province, where the Taliban have long been active, Ahamd Zia Abdulazai, spokesman for the provincial governor, said that a prosecutor and his driver were killed when their vehicle hit a roadside bomb in Behsud district.

On Tuesday, a bomb blast near a police station in the southern city of Kandahar killed three people and wounded 17, while a separate bomb killed one person and wounded five in the north, in Kunduz province. Kandahar province is the heartland of the Taliban insurgency _ and the city was the capital of the extremists' government from 1996-2001. (AP)