Two former U.S. National Security Council experts say military action against Iran could be more damaging to U.S. interests than the struggle in Iraq.

Richard Clarke

Writing in Sunday's New York Times, Richard Clarke and Steven Simon said any pre-emptive U.S. strike could affect global oil prices, de-stabilize Iraq and threaten U.S. interests around the world. 

Clarke is the author of "Against All Enemies," a 2004 book highly critical of the Bush administration's handling of the war on terror.

Meanwhile, a leading U.S. think-tank has released satellite photography purporting to show Iran has reinforced its underground uranium enrichment plant at Natanz.

The imagery published by The Institute for Science and International Security includes four photographs taken between 2002 and 2006. 

The I.S.I.S. said the pictures show Natanz facilities being buried under successive layers of earth and concrete.  Other imagery shows a new tunnel entry to Iran's uranium conversion facility at Isfahan.