The US government has accused Iran of being behind a plot to assassinate the Saudi Arabian ambassador to the US in a sign that relations between the two countries are increasingly strained and look set to deteriorate further.

The US attorney general, Eric Holder, told a news conference on 11 Oct that the Iranian Republican Guards Corps (IRGC) were directly linked to the plot.

Iranian-American Mansoor Arbabsiar, and Gohlam Shakuri, an Iranian official in the Quds Force, the international arm of the IRGC, have been charged with five crimes including conspiracy to murder a foreign official.

Iran has denied any involvement in the plot, and parliamentary speaker Ali Larijani said on 12 October, “These claims are vulgar.”

Prince Turki al-Faisal, a former chief of the Saudi intelligence services, said at a conference in London on 12 October that the evidence of Iranian involvement in the plot was “overwhelming”.