(Adds more from Rice, Miliband at Google event)

By Sue Pleming

PALO ALTO, Calif., May 22 (Reuters) - The United States will aggressively impose more sanctions on Iran as long as it refuses to give up sensitive nuclear work and uses the world's financial system for "terrorism," U.S. Secretary of State Condoleezza Rice said on Thursday.

On a joint trip to California with British Foreign Secretary David Miliband, Rice told reporters the Bush administration assessed "practically every day" whether to slap more sanctions on Iran.

"We will continue to designate entities as we find them trying to use the international financial system for ill-gotten gains and, yes, we are going to continue to do it and we will continue to do it aggressively," said Rice.

"Iran should not be in a position of using the banking system to pass profits made from terrorism or proliferation."

Iran has been subjected to three rounds of U.N. Security Council sanctions over its nuclear program and in October, the United States designated the elite Qods military force of Iran's Revolutionary Guard a supporter of terrorism.

Washington also imposed sanctions on more than 20 Iranian companies, banks and individuals as well as the defense ministry, hoping to increase pressure on Tehran to stop uranium enrichment and curb what the United States views as terrorist activities. Tehran denies the charges against it and says its nuclear program is to produce energy.

Rice said Iran should expect more of these kinds of sanctions but she declined to provide any timeline.

LACK OF TRANSPARENCY

Later, while on a tour of the Internet giant Google in nearby Mountain View, Rice criticized Iran for its lack of transparency with the U.N. nuclear watchdog, which is expected to release a report on Iran's nuclear activities in the coming days.

"If Iran has peaceful intent as they say, then they should have no problem with the International Atomic Energy Agency having complete and absolute and total access. The word that is coming out is that that is not" the case, said Rice.

The five permanent members of the U.N. Security Council -- the United States, France, Britain, China and Russia -- and Germany are awaiting a green light from Iran for a meeting to present a revised package of incentives to get Iran to stop enriching uranium.

The offer was first made to Tehran in 2006 to try to get it to give up uranium enrichment -- a process that can produce fuel for nuclear power plants or atomic bombs -- for a range of economic and diplomatic benefits. Details of the offer have not been made public.

Iran, which is the world's fourth-largest oil producer, has turned down those proposals.

Rice said if Iran rejected the revised incentives package, it would face more sanctions at the United Nations.

However, the United States would face an uphill battle from veto-wielding Security Council members China and Russia, which oppose further punitive measures against Iran.

Miliband said Iran had an important choice and it must accept the consequences of its actions.

"We are making very clear to the world that this is a choice for Iran. Iran can see the outstretched hand from the wider world ready to cooperate economically and technologically and scientifically, but only if Iran respects its responsibilities," said Miliband. (Editing by Frances Kerry and Jackie Frank)

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