Hekmatyar, a former prime minister, told Britain's Daily Telegraph newspaper that fresh attacks would send a warning to "others waiting to invade Afghanistan".

"Before the withdrawal of invading forces, the Mujahideen would like to witness with their own eyes a scene that will teach the invaders to never think of coming this way again," he said in a video obtained by the Telegraph in response to questions asked through an intermediary.

Hekmatyar, designated a global terrorist by the United States, warned that Afghanistan could collapse into bloody civil unrest after NATO troops withdraw, 13 years after the US-led invasion.

"The fact is that the government has failed," said the former premier, who is shown in the video with a white beard and wearing a black turban.

"We might have a dreadful situation after 2014 which no one could have anticipated."

NATO is aiming to train 350,000 Afghan soldiers and police by the end of 2014 to take over responsibility for security.

But trust between the two sides has been seriously undermined by "insider" attacks by Afghan forces that killed more than 60 foreign troops in 2012, and the transition process has been beset by other problems including desertions.

He condemned the Pakistani Taliban's blocking of girls' schooling, which was thrown into the spotlight in October by its attempted murder of 15-year-old education campaigner Malala Yousafzai on her schoolbus.

He insisted that Hezb-i-Islami "consider education is as necessary for girls as it is for boys", though they object to combined male and female classes.

The movement would be ready to take part in Afghanistan's presidential election in 2014 on the condition of a fair vote and a "complete withdrawal of all foreign forces", he added.

The former premier also blasted British troops as American lackeys and said Britain's Prince Harry, who has been serving in Afghanistan since September as an Apache helicopter pilot, as a "jackal" who was "drunk" while on duty.

"The British prince comes to Afghanistan to kill innocent Afghans while he is drunk," Hekmatyar told the Telegraph.

"Britain dragged herself into this unjustified, useless but cruel conflict to please the White House. The British did not gain anything instead they lost blood and treasure."