Taliban movement declared its annual "spring offensive" on Thursday, vowing a final summer of bloody attacks on foreign forces before the 13-year NATO combat mission ends.

Taliban movement declared its annual "spring offensive" on Thursday, vowing a final summer of bloody attacks on foreign forces before the 13-year NATO combat mission ends.

The insurgents said that the offensive, beginning on Monday, would cleanse "the filth of the infidels" from the country, and warned that Afghan translators, government officials and politicians would also be targeted.

The "Khaibar" offensive, named after an ancient battle between Muslims and Jews, will coincide with a planned second round of elections next month to choose a successor to President Hamid Karzai, who has ruled since the fall of the Taliban in 2001.

The 51,000 US-led NATO troops still deployed in Afghanistan are set to withdraw by December, ending a long and costly battle to defeat the rebels, who launched a fierce insurgency after being ousted from power.

A small number of US troops may stay on from next year on a training and “counter-terrorism” mission, but the Taliban warned that the insurgency would continue against even a few thousand US troops.

The Taliban "insists on the unconditional withdrawal of all invading forces... and sees the continuation of its armed Jihad (as) imperative to achieving these goals," said an English-language statement on the group's website.

"If the invaders or their internal stooges believe that reducing the number of foreign forces will dampen our Jihadi fervor then they are sadly mistaken."

It added that attacks during the coming "fighting season" would target US military bases, foreign embassies and vehicle convoys, as well as the Afghan government.