Britain said Iran would face new UN sanctions unless it gives a response by Tuesday to the offer, a British Foreign Office spokesman said.
"We will be disappointed if there (is) no response to the E3 proposals by tomorrow," the spokesman said, referring to proposals formally put to Tehran by Britain, France and Germany.
"We will have no choice but to ask the UN to proceed with further sanctions."
The French foreign ministry echoed that stance, saying the Islamic republic "will have to face new sanctions" if it does not respond positively by Tuesday to the international community's sanctions freeze-for-enrichment freeze offer.
Paris "expressed its disappointment at the lack of a clear response from Iran" to the proposals, the ministry said in a statement.
In New York France's deputy UN ambassador Jean-Pierre Lacroix told AFP: "If we don't get an encouraging response from the Iranians, we will have to show firmness, resort to sanctions as in the past."
EU foreign policy chief Javier Solana earlier Monday held what a spokesman described as "inconclusive" talks with Iran's top nuclear negotiator, Saeed Jalili, after Tehran missed a deadline set by Washington to respond to the proposed trade and economic incentives.
US State Department spokesman Gonzago Gallegos said Jalili told Solana that Tehran would provide a written response on Tuesday.
Senior diplomats from the United States, Britain, France, Germany, Russia and China discussed the latest developments by telephone Monday and agreed to push for new action against Iran if it continued holding out.
"We agreed that in the absence of a positive response, we have no choice but to pursue further measures," Gallegos said.
"We are disappointed that we have not yet received a response from Iran as requested in Geneva on July 19," he said, referring to when the incentive offer was made.
Tehran has steadfastly refused to suspend its uranium enrichment activities, which it says are aimed only at producing fuel for nuclear power production.
The United States and its allies fear the program is a cover for developing nuclear weapons.
The United Nations has imposed three sets of sanctions against Iran over the dispute and is mulling a fourth round of measures.
Iranian state-run television meanwhile reported that in the Solana-Jalili telephone conversation, "both sides agreed to continue talks," and Solana's spokesman said that further contacts between the EU and Iran "are not ruled out in the coming days."
"They also emphasized that preserving this path (talks) needs a positive and constructive atmosphere," the Iran television report said without elaborating.
Solana presented an offer of economic and trade incentives in mid-June, while Iran has put forward its own proposal, an all-embracing package of suggestions to resolve the problems of the world, including the nuclear issue.
Washington had demanded that Iran respond by last weekend to the proposal, while Iran dismissed the deadline as "media speculation."
Amid the continued tensions, Iran announced on Monday that it had successfully test-fired an anti-ship missile with a range of 300 kilometers (180 miles) that it had developed with homegrown technology.
"No enemy vessels would be able to escape it within a 300-kilometer radius from the borders of Iran," said the commander of the elite Revolutionary Guards, General Mohammad Ali Jafari.
Iran has in recent months frequently boasted of developing new weapons and military hardware but the claims have often met with skepticism from Western defense analysts.
