In a series of scenarios drawn up for Pakistan, Frederick Kagan, a former West Point military historian, has called for the White House to consider various options for an unstable Pakistan.

These include: sending elite British or US troops to secure nuclear weapons capable of being transported out of the country and take them to a secret storage depot in New Mexico or a "remote redoubt" inside Pakistan; sending US troops to Pakistan's north-western border to fight the Taliban and al-Qaida; and a US military occupation of the capital Islamabad, and the provinces of Punjab, Sindh and Baluchistan if asked for assistance by a fractured Pakistan military, so that the US could shore up President Pervez Musharraf and General Ashfaq Kayani, who became army chief this week.

"These are scenarios and solutions. They are designed to test our preparedness. The United States simply could not stand by as a nuclear-armed Pakistan descended into the abyss," Kagan, who is with the American Enterprise Institute, a thinktank with strong ideological ties to the Bush administration, told the Guardian. "We need to think now about our options in Pakistan,"

Kagan argued that the rise of Sunni extremism in Pakistan, coupled with the proliferation of al-Qaida bases in the north-west, posed a real possibility of terrorists staging a coup that would give them access to a nuclear device. He also noted how sections of Pakistan's military and intelligence establishment continued to be linked to Islamists and warned that the army, demoralised by having to fight in Waziristan and parts of North-West Frontier Province, might retreat from the borders, leaving a vacuum that would be filled by radicals. Worse, the military might split, with a radical faction trying to take over Pakistan's nuclear arsenal.

Kagan accepted that the Pakistani military was not in the grip of Islamists. "Pakistan's officer corps and ruling elites remain largely moderate. But then again, Americans felt similarly about the shah's regime and look what happened in 1979," he said, referring to Iran.

The scenarios received a public airing two weeks ago in an article for the New York Times by Kagan and Michael O'Hanlon, an analyst at the Brookings Institution, who has ties to the Democrats.

They have been criticised in the US as well as Pakistan, with Kagan accused of drawing up plans for another US occupation of a Muslim country.

But the scenarios are regarded with some seriousness because of Kagan's influence over thinking in the Bush administration as the architect of the Iraq troop surge, which is conceded to have brought some improvements in security.

A former senior state department official who works as a contractor with the government and is familiar with current planning on Pakistan told the Guardian: "Governments are supposed to think the unthinkable. But these ideas, coming as they do from a man of significant influence in Washington's militarist camp, seem prescriptive and have got tongues wagging - even in a town like Washington, built on hyperbole."

Kagan said he was not calling for an occupation of Pakistan.

"I have been arguing the opposite. We cannot invade, only work with the consent of elements of the Pakistan military," he said.

"But we do have to calculate how to quantify and then respond to a crisis that is potentially as much a threat as Soviet tanks once were. Pakistan may be the next big test."

The political and security crises there have led the Bush administration to conclude that Pakistan has become a more dangerous place than it was before Musharraf took over in the coup of October 1999.

One Pentagon official said last week that the defence department had indeed been war-gaming some of Kagan's scenarios.

A report by Kagan and O'Hanlon in April highlighted their argument.

"The only serious response to this international environment is to develop armed forces capable of protecting America's vital interests throughout this dangerous time," it said.

But in Pakistan, aides to Musharraf yesterday dismissed Kagan's study as "hyperbole".