US lawmakers from both the Democrat and Republican parties stepped up pressure on President Barack Obama to level tough new economic sanctions on Iran in the event that Teheran fails to freeze its nuclear program by late 2009, AFP reported on Monday. Republican Senators Jon Kyl and John McCain, Independent Senator Joseph Lieberman, and Democratic Senator Evan Bayh urged the president to prepare sanctions targeting the Central Bank of Iran in the case of a diplomatic stalemate. The four lawmakers introduced a bill calling on the president to act if Iran does not accept his offer of direct talks before a late September summit of the Group of 20 or fails to freeze uranium enrichment and reprocessing activities 60 days after that. "Whether one believes 'engaging' directly with the regime in Teheran will accomplish anything, there is no question that time is of the essence," AFP quoted Kyl, the chamber's number two Republican as saying. "Every day that passes is time that the Iranians use to perfect a nuclear weapon and stockpile nuclear weapons material," said Kyl. The measure, introduced as an amendment to an annual defense spending budget bill, warns of stricter US economic sanctions on Iran's government unless the UN Security Council toughens its own sanctions regime on the Islamic republic. Israel, which pledged not to allow the Iranians to attain nuclear weapons, has been pressing the US administration to put a deadline on Obama's offer of dialogue, worried that Iran would stall while clandestinely pushing ahead with its nuclear agenda. Lieberman, a strong supporter of Israel, said he supported Obama's offer of direct talks but warned that "the Iranians need to understand that this is a limited-time offer." In the recent Group of Eight (G8) summit in Italy, major world powers agreed that they would assess Iran's nuclear cooperation at the G20, to be held in Pittsburgh, Pennsylvania, ahead of the United Nations General Assembly meeting. Iran, already slapped with UN sanctions for refusing to freeze its contested nuclear program, has rejected the West's charges that it seeks nuclear weapons under cover of a civilian atomic energy program. Notwithstanding Iran's insistence that its program is intended to produce cheap energy, Iranian President Mahmoud Ahmadinejad has repeatedly called for Israel to be "wiped off the map" and has also publicly doubted that the Holocaust took place. Obama has said he wants a diplomatic solution to the standoff but has repeatedly warned that he has not ruled out the use of force. His efforts have been complicated by the recent Iranian elections, which many in the West and Iran believe were rigged by the regime, which supports hardliner Ahmadinejad. "This amendment demonstrates that the regime must decide to change course, soon, or face severe sanctions for its continued defiance of the international community," said McCain. And "if Iranian officials are unwilling to sit down at the table and negotiate, then Congress is prepared to authorize crippling economic sanctions," said Bayh.