The insurgency has moved much closer to Kabul, the report says
The Taleban has a permanent presence in nearly 75% of Afghanistan, a new report by an international think-tank says.
The International Council on Security and Development says the insurgents can now infiltrate Kabul at will, although the government rejects the findings.
Taleban leader Mullah Omar has warned violence in Afghanistan will rise and has urged foreign forces to withdraw.
The BBC has also learned that renewed efforts are being made to arrange peace talks with some members of the Taleban.
The International Council on Security and Development says the insurgent group has moved well beyond its southern heartland and is at the gates of Kabul.
"Of the four doors leading out of Kabul, three are now compromised by Taleban activity," it said.
"The increase in their geographic spread illustrates that the Taleban's political, military and economic strategies are now more successful than the West's in Afghanistan."
The US plans to send more troops to Afghanistan next year
Afghanistan's ministry of foreign affairs said it "strongly rejected the assertion on the extent of the Taleban's presence across Afghanistan".
"In addition to the questionable methodology of the report and its conceptual confusion, the report has misinterpreted the sporadic, terrorising and media-oriented activities of the Taleban."
The BBC's Ian Pannell in Kabul says the report is controversial but there is little doubt that violence in Afghanistan has grown and that the insurgency has spread and moved much closer to the capital.
The report comes as renewed efforts are being made to try to instigate peace talks with elements of the Taleban, our correspondent says.
A meeting is being planned in Dubai in the coming days involving 40 or so Afghans, representing both the insurgents and the government.
It is being organised by the son-in-law of one of the country's most notorious pro-Taleban warlords and has the support of Washington, our correspondent report.
However, many are cautioning that this is just a first tentative step and expectations remain low.
'No safe haven'
Meanwhile, a US military spokesman has said that Taleban leader Mullah Omar's first public statement for almost a year suggests he is concerned about rising US troop numbers.
Col Greg Julian agreed with Mullah Omar's warning of more clashes, saying US troops would leave "no safe haven" in Afghanistan for militants.
Col Julian said the Taleban were "most concerned about this increase in troop strength in Afghanistan, which is the last thing they want because they know it will lead to their defeat".
He added: "We're going to take the fight to them."
There are currently 33,000 US troops in Afghanistan.
US President George W Bush has announced that about 4,500 more soldiers will be sent to Afghanistan early in 2009.
In his statement, Mullah Omar, whose whereabouts are unknown, said: "I would like to remind the illegal invaders who have invaded our defenceless and oppressed people that it is a golden opportunity for you at present to hammer out an exit strategy for your forces.
"The current armed clashes which now number into tens, will spiral up to hundreds of armed clashes.
"Your current casualties of hundreds will jack up in to the thousands."