The Taliban said that the offensive will start on Monday and all Afghan nationals working in intelligence, the security forces or the judiciary or any member of the government will be a target.

"The Taliban warned that they will bring the fight to the cities and lay siege to the cities, but pledged to protect civilians during the operation," she added.

Farhad Paykar, an Afghan journalist, said that the timing of the Taliban announcement conveyed two messages - that they are still a strong force to be reckoned with, and that they still have the same position of wanting to fight the Afghan government and foreign forces.

'Propaganda campaign'

General Abdul Rahim Wardakhe, the Afghan defence minister, however, dismissed the Taliban threat as more of a publicity gimmick.

"I doubt seriously that they have the capability to do something like what they claim. I do believe it is a propaganda campaign rather than a reality," he said.

The defence minister also said that, according to their intelligence, most of the Taliban leaders have gone to Pakistan.

But Paykar felt the Taliban threat may not be entirely hollow.

"The Taliban in the past few years have never launched a conventional war - they relied on hit-and-run tactics and have been very successful on this and will increase this," he said.

"We have never seen Taliban leaders at the front-line of wars, so it doesn't matter where the leaders are - it matters where their forces are and how they launch attacks."

Karzai visit

Karzai is hoping that his upcoming meeting with Barack Obama, the US president, will bring renewed legitimacy and the political backing he needs for possible peace talks with the Taliban.

The Washington trip comes at a critical juncture in the war as more troops and aid are moving into the country.

The US is pouring thousands more troops into the country ahead of the planned operation in the southern province of Kandahar, the heartland of the Taliban.

The Taliban has waged a nine-year war against Karzai's Western-backed government since their own administration was overthrown by a US-led invasion in late 2001.