TEHRAN, Iran - More than a third of Iran's parliament has signed on to a bill ordering an acceleration of the country's nuclear program if the U.S. Congress follows through with new sanctions, lawmakers said.

In a gesture apparently intended as retaliation for congressional sanctions legislation, 100 members of Iran's parliament have signed on to a resolution calling for an increase in uranium enrichment to 60 percent purity from a current 20 percent. The bill also would order activation of the partially built Arak heavy-water nuclear reactor, which could generate plutonium that could be used as bomb fuel.

Some U.S. advocates of sanctions maintain the Iranian threats are hollow. Some, including Sen. Robert Menendez (D., N.J.), say that the economic pressure created by past Western sanctions has forced Tehran to the negotiating table and that pressure must be kept on with the threat of further sanctions.

But the legislation was another sign of the continuing tensions between the two sides one month after Iran and six world powers, including the United States, signed a preliminary agreement to freeze some aspects of its nuclear program.

The six world powers have been negotiating with Iran for a decade to try to impose limits on its nuclear program.

Mehdi Moussavinejad, a member of the parliament's energy committee, told the official Fars news agency that the bill would require acceleration of the program if new sanctions are imposed or existing sanctions are "intensified."