Western powers should negotiate a nuclear deal with Pakistan similar to its accord with India as a way to reduce dangers from Islamabad, a prominent expert said Wednesday.

Mark Fitzpatrick, a longtime US diplomat who is now a scholar at the London-based International Institute for Strategic Studies, voiced alarm about Pakistan's nuclear arsenal -- the world's fastest growing -- which he said would likely expand until at least 2020.

Fitzpatrick said no solution was ideal, but he called for Western nations to offer Pakistan a deal along the lines of a 2005 accord with India, which allowed normal access to commercial nuclear markets despite its refusal to sign the Non-Proliferation Treaty.

"The time has come to offer Pakistan a nuclear cooperation deal akin to India's," Fitzpatrick said as he launched a new book, "Overcoming Pakistan's Nuclear Dangers," in Washington.

"Providing a formula for nuclear normalization is the most powerful tool that Western countries can wield in positively shaping Pakistan's nuclear posture," Fitzpatrick said.

Fitzpatrick said that Pakistan faced a "heavier burden of proof" than India to demonstrate it is a responsible power, after the father of Islamabad's bomb, Abdul Qadeer Khan, spread the technology widely, and due to the presence of Islamic extremist groups.

Among conditions for a nuclear deal, Pakistan should stop blocking a new international agreement banning the production of fissile material and join the Comprehensive Nuclear-Test-Ban Treaty, he said.

In the book, Fitzpatrick said the risk of a much-discussed scenario in which Islamic extremists seize nuclear weapons was exaggerated, and that the larger danger was that Pakistan-linked militants would launch a new attack inside India and trigger a devastating nuclear war.

Fitzpatrick, while voicing concern over an arms race, said Pakistan was constrained by its lack of uranium ore. Quoting anonymous sources, Fitzpatrick said Pakistan's production may end in 2020, by which time it would have some 200 nuclear weapons, about double the current estimate.

Fitzpatrick also doubted reports that Pakistan would share nuclear weapons with Saudi Arabia in response to the kingdom's concerns on Iran, saying Islamabad would not want to open potential conflict with another neighbor.

Many experts believe Saudi Arabia funded Pakistan's nuclear program. The South Asian nation went nuclear in 1998 days after a test by arch-rival India.