Violent incidents in the Afghan war have increased by nearly 40 percent over last year, according to UN figures released Wednesday.
But in an unusual step, the NATO-led International Security Assistance Force issued a statement in response saying it found the figures "inconsistent with the data that we have collected".
ISAF is set to give further details Thursday.
The UN figures showed total security incidents averaging 2,108 a month in the first eight months of 2011, up 39 percent on the same period in 2010.
Two thirds of the activity was focused on the southern and southeastern regions, particularly the Taliban birthplace of Kandahar and its surrounds.
A report to the UN Security Council shows that despite US-led efforts to protect ordinary people, the number of civilians killed over the summer rose five percent compared to the same period in 2010.
From June to August, the UN's mission in Afghanistan documented 971 civilian deaths, with three quarters attributed to insurgent violence and 12 percent blamed on NATO's US-led forces. The rest could not be attributed.
Recent multi-pronged attacks in Kabul and high-profile political assassinations over the summer have fed perceptions that after 10 years, the West's war effort is losing a grip on the Taliban's bid to return to power.
The average number of suicide attacks each month was unchanged, but complex suicide attacks made up a greater proportion of the violence, with three such attacks each month in 2011, a 50 percent rise on the same period in 2010.
"In the context of overall intensified fighting" the report said, the rise in violent attacks was mostly due to the use of Taliban bombs and suicide attacks.
Air strikes were the leading cause of civilian deaths by pro-government forces, but the number of those killed through ground combat and armed clashes increased 84 percent on the same time period in 2010.
The deaths of ordinary people in NATO's counterinsurgency campaign has long been a thorny issue for the alliance, with President Hamid Karzai making public rebukes over controversial strikes.
The relentless rise in the scale of killing comes as gradual withdrawals of foreign troops begin, firstly with the removal of some of the 33,000 US "surge" troops who were sent in to turn the war around.
The UN in June reported that civilian deaths in the first half of the year were up 15 percent, putting 2011 on track to be the deadliest in the long war.
Some 130,000 people have been displaced from January 1 until the end of July, the latest report said, an increase of two-thirds on a year before.
However, in brighter news for government efforts to eradicate opium crops, which generate funds for much of the Taliban's efforts, the UN and Ministry of Counter Narcotics reported a 65 percent increase in poppy eradication in 2010.