The United Nations has been urging participants at this weekend's NATO summit to provide "predictable, massive, long-term support" for Afghanistan's security forces to promote stability and ensure that the country is never again a base for international terrorism, the U.N. envoy to Afghanistan said Friday.

In the run-up to the summit in Chicago, the U.N. has been sending "a very strong message" to countries that are _ and are not _ part of the NATO-led coalition in Afghanistan that the heavy investment of the last 10 years, including thousands killed, must not be lost, Jan Kubis said in an interview with The Associated Press.

Ahead of the withdrawal of foreign forces from Afghanistan in 2014, Kubis said, the NATO summit should deliver "a clear commitment of individual countries" _ not just general political pledges _ to contribute as much as possible toward the $4.1 billion annual goal for the Afghan security forces for many years to come.

Afghan President Hamid Karzai has said he estimates that Afghanistan will need $4.1 billion annually to run its security services, of which it could pay $500 million itself and possibly more as its economy strengthens. Kubis said the figure was reached at a meeting co-chaired by the government and the U.N.

Unless there is significant financial support for Afghanistan, Kubis said, "we might face a nasty situation once again, so it's a common strategic interest of all of us."

Kubis, who will be accompanying U.N. Secretary-General Ban Ki-moon to Chicago, said support must also come from regional countries that will be meeting in Kabul on June 14 to discuss confidence-building measures in combatting terrorism, the narcotics trade and promoting investment. Pakistan, China and Iran will attend, he said.

"Afghanistan will be firm and stand firm and stable only if there is support from regional countries," he said.

Kubis said Ban will also assure summit participants that U.N. is prepared to continue its programs to help Afghanistan move towards democracy and to channel support for Afghan security forces, notably the police.

Asked whether whether the transition from international to Afghan-led security forces is taking place too quickly, Kubis said "it's for Afghanistan to determine."

"At this time I would say it's a managed process, even a well-managed process," he said. "We see and we hear positive results and our expectations are that the process will continue."

He said "there are always risks and anxieties" when an international force leaves, but "I would say that's a natural development."

Despite the anxiety in Afghan society, he said the 2014 pullout will means "they have full responsibility for the future of the country and that is always a healthy process."