Militant attacks in Afghanistan, near the Pakistan border, have tripled in some areas, the US military has said.
The 5 September peace deal aimed at ending two years of conflict
The rise in activity comes despite a peace agreement meant to end violence by pro-Taleban militants in Pakistan's North Waziristan border area.
But correspondents say the deal has increased friction with Afghanistan.
Meanwhile, Nato has announced that it will extend its mission in Afghanistan to cover the whole country, taking command of thousands of US troops.
The move will be implemented in the next few weeks, a Nato spokesman said.
On Wednesday, US President George W Bush hosted talks between the presidents of Pakistan and Afghanistan in Washington.
Pakistani President Pervez Musharraf and Afghan President Hamid Karzai are at odds on how to fight the Taleban in their border region, and failed to shake hands or speak to each other at the talks.
A brief White House statement after the three-way talks said the leaders had agreed to "moderation and defeating extremism through greater intelligence sharing, [and] coordinated action against terrorists".
Gen Musharraf meanwhile angrily rejected a leaked document by an official close to the UK Ministry of Defence suggesting his intelligence services, the ISI, indirectly backed terrorism by supporting religious groups in Pakistan.
In a BBC TV interview, Gen Musharraf said his intelligence services were doing an "excellent job" in tracking down and apprehending militants, and that he rejected "200%" calls to dismantle them.
The UK Ministry of Defence said the allegations in no way represented its views or those of the British government.
UK Prime Minister Tony Blair is expected to try to allay Gen Musharraf's concerns at a meeting in London on Thursday.
The Afghan and Pakistani leaders have been at odds on the issue of security in recent months.
Mr Karzai says violence in his country has increased since the Waziristan agreement.
Musharraf and Karzai did not shake hands
The US findings appeared to confirm this.
"There has been an increase in the activity certainly along the border region especially in the south-east areas across from Waziristan... in [Afghanistan's] Paktika and Khost provinces," Lte Col Paradis told a news conference.
There were "in some cases two-fold, in some cases three-fold increases in the number of attacks," he said.
Mr Karzai suggests that Pakistan has turned a blind eye to Taleban supporters using parts of the country to train and launch attacks on Afghanistan, and accuses Pakistan of sheltering former Taleban leaders.
Gen Musharraf says the North Waziristan agreement was necessary to fight the Taleban and strongly rejects Mr Karzai's allegations. He says Pakistan is doing all it can to fight terrorism and, in turn, accuses the Afghan leader of inaction.
The ceasefire was agreed on 31 July and became a peace agreement on 5 September aimed at ending two years of regional conflict.
The pact was also designed to choke off cross-border attacks into Afghanistan.
It is nearly five years since the Taleban were forced from power, but thousands of international troops remain in the country hunting Taleban supporters, who have regrouped.