Julian Borger | Washington | January 31

The Guardian - Washington openly blames Iranian supreme leader Ali Khamenei for first time over Saudi ambassador plot.

The head of US intelligence has warned that there is an increasing likelihood that Iran could carry out attacks in America or against US and allied targets around the world.

The warning from the director of national intelligence, James Clapper, reflects rapidly rising tensions over Iran's nuclear programme after the US and EU announced embargoes on the Iranian oil trade in the past few weeks, Israel leaked details of its preparation for a possible conflict and both the west and Iran boosted their military readiness in the Gulf.

The US plans to send a third aircraft carrier to the region in March, while Iran's military has threatened to block the entrance to the Gulf in the strait of Hormuz and is planning to hold naval exercises there in the next few weeks involving a host of new weapons.

Presenting his annual "worldwide threat assessment" to Congress, Clapper said an alleged plot to blow up the Saudi ambassador in Washington last year, which the US blamed on the Iran's Revolutionary Guard, "shows that some Iranian officials – probably including the supreme leader Ali Khamenei – have changed their calculus and are now more willing to conduct an attack in the United States in response to real or perceived US actions that threaten the regime."

Clapper added: "Iran's willingness to sponsor future attacks in the US or against our interests abroad probably will be shaped by Tehran's evaluation of the costs it bears for the plot against the ambassador as well as Iranian leaders' perceptions of US threats against the regime."