KHOST - Gunmen attacked a military air base in the eastern Afghan province of Khost, officials said on Saturday.

Khost police spokesman Faizullah Ghairat said that three militants had attacked the base, close to the border with Pakistan. One had been killed, while two others were still holding out, he said.

There was no immediate comment from the headquarters of the NATO-led Resolute Support mission in Kabul.

The incident comes just ahead of the normal start of the spring fighting season, when warmer weather brings increased operations by both insurgents and government forces.

Afghan and US officials have warned that Afghanistan will see increased fighting this year as the Taliban steps up an insurgency which has cut the area controlled by the government to below 60 percent.

Earlier this week, the head of US Central Command, General Joseph Votel, asked for more American troops to join the roughly 8,400 already stationed there.

The Afghan interior ministry said that over the past 25 hours, security forces had killed 51 armed militants in counter-terrorism operations across Afghanistan.

In a separate incident in the southeastern province of Zabul, two renegade policemen killed eight colleagues and defected to the Taliban, local officials said, although details of the incident, which occurred last Friday, were unclear.

"They first poisoned them and after that shot and killed all of them," Zabul Governor Bismillah Afghanmal said, adding that the men stole weapons and equipment before defecting.

The Taliban's main spokesman Zabihullah Mujahid denied that the two poisoned their colleagues, saying that they had "prepared the way" for other fighters to attack the checkpoint.

EIGHT COPS KILLED IN ‘INSIDER ATTACK’

Eight local policemen were killed by their colleagues after they were poisoned in their base in southern Afghanistan, officials said Saturday, in a latest so-called "insider attack".

The Taliban claimed responsibility for the incident, which happened in the Nawshar district of southern Zabul province late on Friday, as the militants escalate a deadly winter campaign of violence.

"The infiltrators first poisoned their colleagues and then shot them dead," provincial spokesman Gul Islam Seyal told AFP, adding that the attackers fled the area taking all the weapons and munitions from the base.

The governor of Zabul Bismillah Afghanmal said they had launched an investigation into the incident.

Taliban spokesman Zabihullah Mujahid said in a message to the media that the group's "infiltrators" carried out the attack.

So-called insider attacks - when Afghan soldiers and police turn their guns on their colleagues or on international troops - have been a major problem during the more than 15-year-long war.

Such attacks have sapped morale and caused deep mistrust within security ranks.

In a similar incident last month, an Afghan policeman linked to the Taliban shot dead 11 of his colleagues at a checkpoint in the neighboring Helmand province.

And last September, two Afghan soldiers with suspected Taliban links killed at least 12 of their comrades as they slept in the volatile northern province of Kunduz.