KABUL (AFP) — The Taliban last year "seriously rejoined the fight" in Afghanistan, an NGO security group said in a report that concluded the country was "at the beginning of a war, not the end of one."

It has also become clear that the Taliban's "easy departure" in 2001, when a US-led invasion drove them from power, was "more of a strategic retreat than an actual military defeat," the Afghanistan NGO Safety Office (ANSO) said.

"A few years from now, 2007 will likely be looked back upon as the year in which the Taliban seriously rejoined the fight and the hopes of a rapid end to conflict were finally set aside by all but the most optimistic," ANSO said.

About 1,980 civilians were killed in 2007 -- half by insurgents and the rest almost equally by soldiers or criminal groups, the group said.

Insurgents killed 15 NGO workers, four of them foreigners, last year, compared with 24 in 2006 and eight in 2005, the group said. Eighty-eight NGO staffers were abducted in 2007, most of them by insurgents, out of a total 555 kidnappings, it said, without providing numbers for previous years.

Abductions and killings were likely to escalate this year, with growing links between insurgents and criminal gangs increasing the threat, ANSO said.

The NATO-led International Security Assistance Force (ISAF), which is helping the government fight insurgents, is "in fact just now entering a period of broad and deep conflict, the outcomes of which are far from certain," it said.

ISAF may number about 41,000 soldiers but "realistically" could not have more than up to 7,000 for combat, with the rest mostly support staff or prevented from fighting because of national restrictions, the group said.

The size of the Taliban force was unknown, but estimates ranged from 2,000 to 20,000.

"There would not appear to be any capacity within ISAF to stop or turn back anticipated AOG (armed opposition groups) expansion," the report said.

"In simple terms, the consensus amongst informed individuals at the end of 2007 seems to be that Afghanistan is at the beginning of a war, not the end of one."