Iran says it has stopped selling crude oil to France and Britain, in an apparent retaliatory move against the European Union for its phased ban on Tehran's crucial fuel exports.

Iran's Oil Ministry said Sunday that all shipments to French and British companies have ceased and that the Islamic Republic has taken steps to deliver its crude to new customers.

The move appeared designed to preempt an EU decision to stop importing Iranian oil from July 1. The embargo is part of Western efforts to put financial pressure on Tehran for its disputed nuclear program, which the West says is aimed at building atomic weapons. Iran denies this.

The targeted cut is not expected to significantly affect France or Britain, but is seen as a warning to other EU nations more exposed to disruptions in Tehran's oil exports, such as Italy, Spain and Greece.

The 27-nation EU accounts for about 18 percent of Iran's crude exports, the vast majority of which go to Asian countries, mainly China and India.

Also Sunday, U.S. National Security Advisor Tom Donilan was meeting Israeli leaders in Jerusalem amid rising tensions over Iran's nuclear program and reports Israel might be preparing a military strike.

The chairman of the U.S. Joint Chiefs of Staff, General Martin Dempsey, said an Israeli attack on Iran's nuclear facilities would not be “prudent.” In an interview with CNN Sunday, the general said a military strike would be “destabilizing” and would not achieve Israel's long-term objectives.

In London, British Foreign Secretary William Hague also warned that a preemptive Israeli strike would not be “wise,” saying economic sanctions and negotiations had to be given “a real chance” to convince Tehran to abandon its nuclear ambitions.

On Saturday, Vienna-based diplomats said Iran is ready to expand its uranium enrichment program at an underground facility built inside a mountain near the city of Qom.

The diplomats – speaking on the condition they remain anonymous – said Iran is poised to install thousands of new centrifuges at its Fordo enrichment site. The new centrifuges could speed up the production of enriched uranium, which can be used to make nuclear weapons if the uranium is a very high grade.

Inspectors from the International Atomic Energy Agency are due to visit Iran Monday.

Iranian state media reported last week that President Mahmoud Ahmadinejad was set to formally declare the Fordo site “fully operational.” Iran also unveiled what it said are a new generation of centrifuges at a uranium enrichment plant in the central city of Natanz.