The threats of war unless the Taliban surrendered Osama bin Laden were passed to the regime in Afghanistan by the Pakistani government, senior diplomatic sources revealed yesterday.

The Taliban refused to comply but the serious nature of what they were told raises the possibility that Bin Laden, far from launching the attacks on the World Trade Centre in New York and the Pentagon out of the blue 10 days ago, was launching a pre-emptive strike in response to what he saw as US threats.

The warning to the Taliban originated at a four-day meeting of senior Americans, Russians, Iranians and Pakistanis at a hotel in Berlin in mid-July. The conference, the third in a series dubbed "brainstorming on Afghanistan", was part of a classic diplomatic device known as "track two".

It was designed to offer a free and open-ended forum for governments to pass messages and sound out each other's thinking. Participants were experts with long diplomatic experience of the region who were no longer government officials but had close links with their governments.

"The Americans indicated to us that in case the Taliban does not behave and in case Pakistan also doesn't help us to influence the Taliban, then the United States would be left with no option but to take an overt action against Afghanistan," said Niaz Naik, a former foreign minister of Pakistan, who was at the meeting.

"I told the Pakistani government, who informed the Taliban via our foreign office and the Taliban ambassador here."

The three Americans at the Berlin meeting were Tom Simons, a former US ambassador to Pakistan, Karl "Rick" Inderfurth, a former assistant secretary of state for south Asian affairs, and Lee Coldren, who headed the office of Pakistan, Afghan and Bangladesh affairs in the state department until 1997.

According to Mr Naik, the Americans raised the issue of an attack on Afghanistan at one of the full sessions of the conference, convened by Francesc Vendrell, a Spanish diplomat who serves as the UN secretary general's special representative on Afghanistan. In the break afterwards, Mr Naik told the Guardian yesterday, he asked Mr Simons why the attack should be more successful than Bill Clinton's missile strikes on Afghanistan in 1998, which caused 20 deaths but missed Bin Laden.

"He said this time they were very sure. They had all the intelligence and would not miss him this time. It would be aerial action, maybe helicopter gunships, and not only overt, but from very close proximity to Afghanistan. The Russians were listening to the conversation but not participating."

Asked whether he could be sure that the Americans were passing ideas from the Bush administration rather than their own views, Mr Naik said yesterday: "What the Americans indicated to us was perhaps based on official instructions. They were very senior people. Even in 'track two' people are very careful about what they say and don't say."

In the room at the time were not only the Americans, Russians and Pakistanis but also a team from Iran headed by Saeed Rajai Khorassani, a former Iranian envoy to the UN. Three Pakistani generals, one still on active service, attended the conference. Giving further evidence of the fact that the Berlin meeting was designed to influence governments, the UN invited official representatives of both the Taliban government in Kabul and the anti-Taliban Northern Alliance. Dr Abdullah Abdullah, the Northern Alliance's foreign minister, attended. The Taliban declined to send a representative.

The Pakistani government took the US talk of possible strikes seriously enough to pass it on to the Taliban. Pakistan is one of only three governments to recognise the Taliban.

Mr Coldren confirmed the broad outline of the American position at the Berlin meeting yesterday. "I think there was some discussion of the fact that the United States was so disgusted with the Taliban that they might be considering some military action." The three former US diplomats "based our discussion on hearsay from US officials", he said. It was not an agenda item at the meeting "but was mentioned just in passing".

Nikolai Kozyrev, Moscow's former special envoy on Afghanistan and one of the Russians in Berlin, would not confirm the contents of the US conversations, but said: "Maybe they had some discussions in the corridor. I don't exclude such a possibility."

Mr Naik's recollection is that "we had the impression Russians were trying to tell the Americans that the threat of the use of force is sometimes more effective than force itself".

The Berlin conference was the third convened since November last year by Mr Vendrell. As a UN meeting, its official agenda was confined to trying to find a negotiated solution to the civil war in Afghanistan, ending terrorism and heroin trafficking, and discussing humanitarian aid.

Mr Simons denied having said anything about detailed operations. "I've known Niaz Naik and considered him a friend for years. He's an honourable diplomat. I didn't say anything like that and didn't hear anyone else say anything like that. We were clear that feeling in Washington was strong, and that military action was one of the options down the road. But details, I don't know where they came from."

The US was reassessing its Afghan policy under the new Bush administration at the time of the July meeting, according to Mr Simons. "It was clear that the trend of US government policy was widening. People should worry, Taliban, Bin Laden ought to worry - but the drift of US policy was to get away from single issue, from concentrating on Bin Laden as under Clinton, and get broader."

Mr Inderfurth said: "There was no suggestion for military force to be used. What we discussed was the need for a comprehensive political settlement to bring an end to the war in Afghanistan, that has been going on for two decades, and has been doing so much damage."

The Foreign Office confirmed the significance of the Berlin discussions. "The meeting was a bringing together of Afghan factions and some interested states and we received reports from several participants, including the UN," it said.

Asked if he was surprised that the American participants were denying the details they mentioned in Berlin, Mr Naik said last night: "I'm a little surprised but maybe they feel they shouldn't have told us anything in advance now we have had these tragic events".

Russia's president Vladimir Putin said in an interview released yesterday that he had warned the Clinton administration about the dangers posed by Bin Laden. "Washington's reaction at the time really amazed me. They shrugged their shoulders and said matter-of-factly: 'We can't do anything because the Taliban does not want to turn him over'."