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" of Tehran's sponsorship of terrorism."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.RELATED:Jewish communities hail thwarting of Iran terror plotIAEA expected to give details on Iran atom bomb fearsIran tells Turkey: Change tack or face troubleClinton 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."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 already on edge over Iran's nuclear ambitions.Also on Wednesday, the US Treasury said it designated Mahan Air, a commercial Iranian airline, as providing logistical and financial support for Iran's elite forces, which Washington has accused of plotting to kill the Saudi ambassador. "Mahan Air provides transportation, funds transfers and personnel travel services to the (Islamic Revolutionary Guard)," Treasury said in a statement.