In Brussels, diplomats said the EU governments have reached a preliminary agreement on an oil embargo against Iran but are debating when it should come into force.

State Department spokeswoman Victoria Nuland summed it up as "very good news and the result of lots of consultations among us, between the US and EU countries."

She said the development is "very very welcome, and supportive of the intent of the Congress when it passed the new legislation at the end of the year."

US President Barack Obama on the final day of 2011 signed into law tough new sanctions targeting Iran's central bank and financial sector, in a move that could intensify a brewing Gulf showdown.

The sanctions are meant to hit Iran's crucial oil sector and require foreign firms to make a choice between doing business with Tehran's financial sector and central bank or the mighty US economy.

Nuland hoped for even broader sanctions.

"So these (EU measures) are the kinds of steps that we would like to see not just from our close allies and partners in places like Europe but from countries around the world," she said.

"Because we do believe that this is consistent with tightening the noose on Iran economically," she said, adding: "We think that the place to get Iran's attention is with regard to its oil sector."

"It's at this occasion I hope that we can adopt this embargo on Iranian oil exports. We are working on this and things are on track," he said, addressing a press conference with Portuguese counterpart Paolo Portas.

"We have to reassure some of our European partners who purchase Iranian oil. We have to provide them with alternative solutions. But these alternative solutions exist and I think we can attain the objective by the end of January," he said.

A European diplomat in Brussels earlier told AFP: "There is an agreement in principle to forge ahead" with the embargo, but added "there is still a lot of work" to agree on the timing of its implementation ahead of the January 30 meeting.

The EU had been divided over whether to impose an Iranian oil ban, but a breakthrough was reached late December after Greece, Spain and other nations that import Iran's crude lifted their objections, another diplomat said.

Britain and France have pushed for an embargo to punish Iran over its controversial nuclear programme, which Western powers say is aimed at building an atomic bomb. Tehran rejects the charges.

EU governments are now negotiating when the embargo should come into force, the diplomats said.

Oil from Iran in 2010 amounted to 5.8 percent of total EU imports, making Tehran the bloc's fifth-largest supplier after Russia, Norway, Libya and Saudi Arabia.

Spain represents 14.6 percent of Iranian oil imports to Europe, Greece 14.0 and Italy 13.1 percent.

Iran meanwhile renewed on Wednesday a warning to America against keeping a US naval presence in the oil-rich Gulf, underlining a threat that Washington has dismissed as a sign of "weakness."

"The presence of forces from beyond the (Gulf) region has no result but turbulence. We have said the presence of forces from beyond the region in the Persian Gulf is not needed and is harmful," Defence Minister Ahmad Vahidi said, according to state television's website.

Iran has just finished 10 days of naval exercises near the strategic Strait of Hormuz, at the entrance of the Gulf, meant to show it was capable of controlling the channel and closing it if necessary. Twenty percent of the world's oil ships through the strait.

The exercises climaxed on Monday with the test-firing of three types of anti-warship missile.

But the US Defence Department said it would continue the rotation of its 11 aircraft carriers to the Gulf to support regional military operations and keep the Strait of Hormuz open.

"We are committed to protecting maritime freedoms that are the basis for global prosperity; this is one of the main reasons our military forces operate in the region," it said in a statement.