The US is escalating against Iran in its accusation the Tehran was behind a plot to kill the Saudi ambassador in Washington

US Secretary of State Hillary Clinton said on Wednesday that Iran’s alleged ties to a plot to kill the Saudi ambassador in Washington marked a “dangerous escalation” an expression echoed by the Israeli US envoy.

"This plot, very fortunately disrupted by the excellent work of our law enforcement and intelligence professionals, was a flagrant violation of international and US law and a dangerous escalation of the Iranian government's longstanding use of political violence and sponsorship of terrorism," Clinton told a think tank audience in Washington.

Clinton said Iran's alleged part in the conspiracy, which was revealed by US law enforcement officials on Tuesday, showed Tehran was willing to flout established international conventions on protecting diplomats that it itself had signed.

Iran on Wednesday dismissed the US charges that Iran had planned bomb blasts at the Saudi and Zionist regime embassies in Washington, calling them “already failed, funny and ridiculous scenarios.”

"This kind of reckless act undermines international norms and the international system. Iran must be held accountable for its actions," Clinton said, noting that the United States had already imposed targeted sanctions on "individuals within the Iranian government who are associated with this plot and Iran's support for terrorism."

"We will work closely with our international partners to increase Iran's isolation and the pressure on its government and we call upon other nations to join us in condemning this threat to international peace and security," she said.

Saudi Arabia said on Wednesday Iran would "pay the price" for the alleged plot, while Tehran called the accusation a fabrication designed to sow discord in the region.

Israeli Ambassador to the United States Michael Oren said that Israel is taking the “thwarted plot” seriously, saying it was "definitely an escalation" in an interview with MSNBC.

"We know the Iran regime. This is an Iranian regime that has not only sponsored terrorist organizations in our area, Hamas and Hezbollah, that have fired thousands and thousands of rockets at our civilian population, but they've struck abroad as well," Oren said in the interview.

He said this was "definitely an escalation", adding that "it's not out of character for the Iranian regime; this is not a rational regime".

When asked whether Israel is going to take action against Iran, Oren told MSNBC "we are always fighting against Iranian terror at our borders and beyond our borders, and we're always vigilant and we have very good partners in the security and law enforcement institutions of the United States."

The ambassador applauded the U.S.'s success in thwarting the alleged Iranian plot. "But I think the important thing to keep in mind is Iran is doing all of this without nuclear weapons. Imagine what they could do if they actually had nuclear weapons," he warned in the interview.