Iran seems bent on confirming that it is the world’s chief bully and outlaw, the greatest threat to world peace. Its pursuit of nuclear weapons capability, support for international terrorism, and disregard for international law are crystal clear. The international community has used a mix of diplomacy and economic sanctions to try to modify Iranian behavior. But Iranian defiance demands stronger measures. Legislation currently before the United States Congress would significantly ratchet up the pressure.

The terrorist traits of the Iranian regime were exposed again in October, when American officials revealed an Iranian plot to assassinate the Saudi ambassador to the U.S. The crime was to have taken place in a crowded, upscale Washington restaurant, and had it come off, many more would have been killed. According to government informants, attacks were also planned on the Saudi and Israeli embassies in Washington and in Buenos Aires-recalling the 1994 bombing of the AMIA Jewish Center in Argentina’s capital that killed 85 people and was also carried out on Iranian orders. Indeed, Iran’s Defense Minister, Ahmad Vahidi, is wanted by Interpol in connection with the AMIA bombing.

The assassination plot was “directed and approved by elements of the Iranian government and, specifically, senior members of the Quds Force” declared Attorney General Eric H. Holder Jr., who added that “high-up officials” in agencies that are “an integral part of the Iranian government, were responsible for this plot” to strike in the heart of Washington.

Then, on Nov. 8, the International Atomic Energy Agency (IAEA) issued a report stating that while it has not yet produced a bomb, “Iran has carried out activities relevant to the development of a nuclear explosive device.” This was not nuclear technology for peaceful purposes, as Iran’s government claims, but mechanisms “specific to nuclear weapons.”

This information came from the IAEA, the United Nation’s nuclear watchdog, not from the intelligence branch of any particular nation, as had been the case with the allegations about Saddam Hussein’s nuclear plans that led to the second Iraq war. The State Department called the report “comprehensive, credible, quite damning, and alarming.” An Iranian nuclear weapon carried by missiles would endanger Saudi Arabia, the Gulf States, Israel and even Europe-not to mention wreaking havoc with the world’s oil supplies.

Most recently, on Nov. 29, after Great Britain ratcheted up its own sanctions by banning all dealings with Iran’s Central Bank-on which the country’s oil exports depend-dozens of Iranians stormed two British embassy locations in Tehran and wreaked havoc, while several hundred more Iranians demonstrated outside, chanting “Death to Britain!” For anyone old enough to remember what happened to the U.S. embassy there in 1979, and the 444-day hostage ordeal of its 52 occupants, this latest attack brought back nightmarish memories. Certain that Iranian authorities were behind this breach of international law, British Foreign Secretary William Hague warned of “serious consequences.”

The British shut their embassy and expelled all Iranian diplomats from London. Several European governments joined by withdrawing their ambassadors from Iran in protest. While Russia and China are unlikely to follow suit, surely the EU as a unit should call its ambassadors home, just as it did in 2009 to protest a coup that ousted the lawful government of Honduras. (The U.S. does not have a diplomatic mission in Iran.)

The industrialized nations must emulate the British by adopting more stringent measures against Iran’s banking system and oil industry. There is reason to believe this will have an impact. The most recent poll of Iranian opinion, the December 2010 survey released by the International Peace Institute, notes that while most Iranians support the nuclear program, they consider the existing economic sanctions the country’s number one external problem, and by 65 percent to 32 percent think that Iran should focus on solving its domestic problems rather than on becoming the leading power in the region.

The Menendez-Kirk Iran Sanctions Amendment, passed unanimously by the U.S. Senate, would restrict American financial institutions from dealings with any foreign financial institution that knowingly does significant business with Iran’s Central Bank. It also freezes Iranian assets in the U.S. and requires the president to engage in diplomacy to convince other nations to cease importing oil from Iran. The U.S. does not, but the EU accounts for 18 percent of Iranian oil exports. While the House of Representatives has passed a version of the bill, the Administration is apparently trying to weaken the sanctions before it becomes law.

That would be a mistake. Menendez-Kirk, with tough sanctions and vigorous enforcement, will signal to the Iranian regime that violation of treaty obligations and Security Council sanctions in pursuit of nuclear weapons will come at a heavy, unsustainable price. And, U.S. leadership will encourage European and other nations to act similarly. With each passing day, Iran makes further progress in it nuclear weapons program. Strong diplomatic isolation and economic sanctions can stop the momentum.

Nancy Lisker is Regional Director of the American Jewish Committee.