“This has shown the resolve of the European Union on this issue and of the international community, and it is absolutely the right thing to do,” said the British foreign secretary, William Hague, who added that the details would be made public later Monday. It was, he said, “an important decision and it will be a major strengthening of the sanctions applied.”

Under the deal, the members agreed not to sign new oil contracts with Iran and to end existing ones by July 1, the ministers said in a statement.

The embargo will cover imports of crude oil, petroleum products and petrochemical products. It will also cover the export of key equipment and technology for the sector.

The assets of the Iranian central bank within the European Union will be frozen with limited exemptions to permit the continuation of legitimate trade, the statement said.

One exemption was designed to allow the execution of existing oil contracts, said one diplomat who was not authorized to speak publicly.

“Trade in gold, precious metals and diamonds with Iranian public bodies and the central bank will no more be permitted, nor will the delivery of Iranian-denominated banknotes and coinage to the Iranian central bank,” the ministers’ statement said. “A number of additional sensitive dual-use goods may no more be sold to Iran.”

The accord allows for a review, to be made before May 1, of the economic impact of the sanctions on countries, including Greece, which rely heavily on Iranian oil. Greece has sought more time to find new sources of oil to soften the impact on its debt-crippled economy.

Despite giving some flexibility for Greece, the decision was a significant escalation of the confrontation with Iran over fears that it is seeking nuclear weapons capability. In recent years, Tehran has faced an expanding catalog of economic penalties imposed by the United Nations, European nations and the United States. It was not clear what the European nations planned to do next if Iran simply rejected the latest measures.

“These tough sanctions are an essential next step in making clear that we expect Tehran to change its ways and to prove that its nuclear program is not arms related,” the Dutch foreign minister, Uri Rosenthal, said. “Now is not the time to speculate on any further measures or whether they are on the table or not.”

Iran insists that its nuclear program is for civilian uses only and has threatened to retaliate against intensifying sanctions by blocking the Strait of Hormuz, a strategic corridor for Western energy supplies.

Diplomats say there is a risk that governments in Asia, which rank among Iran’ s most important customers for its oil, will step in to fill the gap left by European buyers and the West is expected to increase efforts to persuade them not to do so.

Mr. Hague also said that the European Union was committed to a dual-track strategy and was open to negotiations with the Iranians over their nuclear program.

The meeting took place against a backdrop of growing tension between Iran and the West over the nuclear enrichment program. The standoff has promoted fears that the dispute could escalate with a military strike against Iran’s nuclear facilities.

Mr. Hague said the measures undertaken by the European Union were “peaceful and legitimate measures.”

“They are not about conflict,” he said. “I hope Iran will come to its senses on this issue and agree to negotiate.”

In recent days Iran has signaled readiness to resume talks suspended a year ago in Turkey with the United States, China, Russia, France, Germany and Britain. But its terms for resuming the talks were not clear.

Reinforcing Western diplomacy with a display of military muscle, an American aircraft carrier, the Abraham Lincoln, steamed through the Strait of Hormuz into the Persian Gulf, the United States Navy reported on Sunday. The British Ministry of Defense said later that it was accompanied by British and French warships.

About one-fifth of the world’s oil supplies passes through the strategic strait, and Iran has in the past said it would respond to tightened sanctions by closing it.

“Any attempt to close the Strait of Hormuz would be illegal and I believe would be unsuccessful,” Mr. Hague said on Monday.

Stephen Castle reported from Brussels, and Alan Cowell from London.

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