A top American defence official has warned that the level of violence in Afghanistan will go on rising.
Fighting in Afghanistan continues to attract international criticism
General Michael Maples said that insurgents had expanded their operations and abilities even while incurring serious combat losses.
Gen Maples is head of the US Defence Intelligence Agency.
More than 3,000 people have died in fighting in Afghanistan this year, according to the New York-based Human Rights Watch.
Gen Maples told a Congressional hearing that the insurgents in Afghanistan had strengthened their influence with their core base of Pashtun communities.
"Violence this year is likely to be twice as high as the violence level seen in 2005. In 2007, insurgents are likely to sustain their use of more visible, aggressive and lethal tactics," he was quoted saying by the AFP news agency.
The head of the CIA, General Michael Hayden defended the government of President Hamid Karzai.
"Kabul needs help because it lacks capacity, not because it lacks political will or lacks support," Gen Hayden told the hearing.
"President Karzai understands this and recognises his government's responsibility."
There has been a four-fold rise this year in the number of people killed in the conflict in Afghanistan, according to a report on the insurgency released on Monday.
Opium poppies are a key source of income for many farmers
Separately, a US government study has warned that the prevalence of opium cultivation and drug trafficking in Afghanistan threatened the stability of the government.
The report by the Government Accountability Office also warned that the deteriorating security situation in Afghanistan could derail a US anti-drug programme.
Afghanistan is the world's largest supplier of opium, and drug money is reportedly fuelling the insurgency.
The report claimed that the Usaid's programme to eradicate drugs was making only limited progress - opium cultivation grew by 50% this year while staff attempting to eradicate drugs or administer alternative uses for land had been attacked and in some cases killed.