The Taliban hold a permanent presence in 72 percent of Afghanistan, a think-tank said on Monday, but NATO and the Afghan government rejected the report, saying its figures were not credible.

The findings by the International Council on Security and Development (ICOS) come in the wake of a series of critical reports on Western-led military and development efforts to put an end to the seven-year Taliban insurgency in Afghanistan.

The U.S. government is conducting a wide-ranging review of strategy aimed at countering the Taliban guerrilla and bombing campaign which analysts agree has grown in both scale and scope in the last year.

But while the trends in the ICOS report reflected prevailing sentiment on Afghanistan, many of its findings appeared flawed and contained some glaring errors, security analysts said.

"The Taliban now has a permanent presence in 72 percent of the country," ICOS, formerly known as the Senlis Council, said in the report, adding that the figure had risen from 54 percent last year.

ICOS is an independent think-tank and research organization based in Brazil that has researchers in the region.

The report defines a permanent presence as an average of one or more insurgent attacks per week over the entire year.

According to ICOS, a "permanent presence" then would include many areas of the country where the Taliban traditionally launch a large number of attacks in the spring and summer "fighting season," before melting away during the harsh winter months.