"The agenda is to reinforce our diplomatic effort," Rice told a news conference here after talks with Greek Foreign Minister Dora Bakoyannis.

"The US president does not take any options off the table, but we are on a diplomatic course here, that is the agenda that we are pursuing, that is the agenda the foreign minister and I discussed," she said.

Rice's comments came after Iranian President Mahmoud Ahmadinejad said Monday that his nation would not comply with a UN Security Council demand to freeze uranium enrichment by the end of this week.

And earlier Tuesday, top nuclear negotiator Ali Larijani said that Iran will suspend its relations with the UN's atomic watchdog if sanctions are imposed.

"If you decide to use sanctions against us, our relations with the agency will be suspended," Larijani said of the International Atomic Energy Agency (IAEA).

In Athens, Rice countered that "the Iranians can threaten, but they are deepening their own isolation."

"I would just say that when the international community speaks, and says that a member state must do something, then the international community has to be credible about that demand," she said.

"We will return to the UN Security Council after the report of the IAEA. ... We will consider what measures to take next, but we can't have another presidential statement, particularly in the light of Iran's continued defiance of international norm."

She was apparently referring a March 29 Security Council document giving Iran a month to completely halt its uranium enrichment activities.

As talks between Bakoyannis and Rice were under way, police stationed around 300 metres (yards) from the foreign ministry used tear gas to disperse a left-wing demonstration of about 400 people who were attempting to break through en route to the US embassy.

A larger communist demonstration of a few thousand decided against forcing the police cordon, and turned back.

The marchers held banners proclaiming support for the Iraqi resistance forces and opposition to military intervention in Iran.

"Wanted for killing millions of people," read a banner with Rice's picture, while another played on the secretary of state's surname, replacing Rice with 'Reich' in a reference to the Nazi German regime during World War II.

Some of the scattered protesters later caused damage at shops and cars in the area, Net state television reported.

A total of around 5,000 police officers were deployed around town to regulate traffic and guard approaches to the Greek parliament, the prime minister's residence, the foreign ministry and the US embassy.

During Rice's presence in the area, police helicopters flew overhead, and even pedestrians were prevented from nearing within a block of government buildings.

After talks with Greek Prime Minister Costas Karamanlis, the secretary of state is expected to spend an hour at the US embassy before departing for Ankara at 14:45 pm (1145 GMT).

Rice's visit to Athens is the first by a US secretary of state for bilateral talks since 1986, when George Schultz held the post under the Reagan administration.

During the Clinton administration, Warren Christopher visited Athens for a NATO meeting.

But Rice's immediate predecessor Colin Powell cancelled planned visits to the Greek capital on three occasions in 2004 and 2003.

All rights reserved. © 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.