KABUL - The Taliban said Wednesday they will start their spring offensive this week, an annual campaign in their war against the Afghan government.

In a statement emailed to media, the group said the offensive -- dubbed “Azm” or perseverance in Dari and Arabic -- will begin on Friday. The Taliban said their Islamic Emirate of Afghanistan is “determined to prolong the ongoing jihad,” or holy war.

In past years, spring and the melting of snow on the mountains along the border with Pakistan have marked a significant upsurge in fighting between the Taliban and NATO forces along with their local allies.

This fighting season is the first year the insurgents will face just Afghan forces on the battlefield after the withdrawal of most international combat troops at the end of last year.

While a long-term demand of the group has been the withdrawal of international military from Afghanistan, the statement 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, advise and assist” the 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 statement says.

In recent weeks, attacks across the north and east of the country have intensified in the build-up to the launch of this year's 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. This has alarmed many Afghans, including influential warlord Ismail Khan, former governor of western Herat province.

Khan has called on President Ashraf Ghani to improve security and kickstart a moribund economy in Afghanistan in order to avoid a war with an IS offshoot.

Afghan forces have been fighting local Taliban in southern Helmand province for more than two months, 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 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.

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.

Associated Press writer Rahim Faiez in Kabul contributed to this story.