Saudi Arabia intends to buy an "off the shelf" nuclear weapon from Pakistan, according to US officials quoted in The Sunday Times.

The report comes amid ongoing negotiations between Iran and other world powers over its nuclear programme, and a potential thawing of relations between the US and Iran.

Saudi Arabia is wary of a potential deal on Iran's nuclear programme and Prince Turki bin Faisal, the former Saudi intelligence chief, has warned that it could pave the way for nuclear proliferation in the region.

The Sunday Times report suggests that Saudi Arabia has already taken the decision to acquire a nuclear device from its ally Pakistan.

The report quotes an anonymous US defence official as saying: “There has been a longstanding agreement in place with the Pakistanis [over nuclear weapons] and the House of Saud has now made the strategic decision to move forward.”

Saudi Arabia is believed to have helped fund Pakistan's nuclear programme, which began back in the 1970s. Pakistan tested its first nuclear device in 1998.

Pakistani officials deny allowing Saudi Arabia access to the country's nuclear technology.

Negotiators have yet to reach a deal on Iran's nuclear programme, but if they do it could leave Iran's 5,000 centrifuges and much of its research programme in place.

The Gulf States warn that any deal that leaves open the possibility Iran could eventually enrich uranium to weapons grade would promote a nuclear arms race in the region.