The leader of the Afghan Taliban on Friday called on followers to end divisions and rally behind him in the battle against the Kabul government as authorities step up the fight against the 15-year-old insurgency.

In a message distributed to media, Mullah Akhtar Mansoor claimed the Taliban were winning the war and were "in a better state than at any other time."

The Taliban were toppled in the 2001 U.S. invasion of Afghanistan. The insurgency has escalated since the end in 2014 of the U.S.-NATO combat mission left inexperienced Afghan forces to battle the insurgents largely on their own.

As the Taliban launched their annual warm-weather offensive last year, the government responded with large-scale military operations. Ferocious battles have raged in the militants' southern heartland of Helmand province and elsewhere.

Separately, Afghan President Ashraf Ghani had been hoping to revive a stalled peace process with face-to-face talks earlier this month with Taliban representatives. The Taliban issued a statement last week saying they would not participate.

Referring to Afghanistan as the Islamic Emirate, Mansoor said that all efforts must be made to reunite the Taliban, split since last summer when they admitted that their founder and leader, Mullah Mohammad Omar, had been dead for more than two years.

Mansoor, previously Mullah Omar's deputy, took over amid much controversy and rifts soon emerged, leading to infighting that has damaged the united Taliban front they had cultivated for so long. Much of the infighting is over control of lucrative smuggling routes through to Pakistan for drugs, minerals, arms and men.

Referring to the "brothers who grew upset over the past year or remained at a distance from the Islamic Emirate," Mansoor said everything should be done to "placate, assuage and integrate them back into the united fold."