SPECIAL CORRESPONDENT WASHINGTON - Military action against Iran could have 'unintended consequences in the region, US Defence Secretary Leon Panetta has warned. While a military option must be kept available, it might not result in really deterring Iran from what they want to do, he said at a Pentagon press conference. Youve got to be careful of unintended consequences here, Panetta said. It could have a serious impact in the region and it could have a serious impact on US forces in the region, he said. His warning came hours after Iran warned that an attack against its nuclear sites would be met by 'iron fists. Panetta , who took over the Pentagons top job in July, said he agreed with an assessment of his predecessor, Robert Gates, that a strike on Iran would only delay its nuclear programme, which the West claims is aimed at making an atomic bomb. Gates also warned it could unite the country and deepen its resolve toward pursuing nuclear weapons. Iran says its nuclear programme is peaceful and that it is enriching uranium to power reactors for electricity generation. Panetta acknowledged military action might fail to deter Iran from what they want to do. And he added: 'But more importantly, it could have a serious impact in the region, and it could have a serious impact on US forces in the region. And I think all of those things, you know, need to be carefully considered. Tension over Irans nuclear programme have increased since Tuesday when the International Atomic Energy Agency (IAEA) reported that Tehran appeared to have worked on designing a bomb and may still be conducting secret research to that end. Speculation has heightened in the Israeli media that Israel may strike Irans nuclear sites and there is speculation in the Western press about a possible US attack. Iran has warned that it will respond to any attacks by hitting Israel and US interests in the Gulf. Analysts say Tehran could retaliate by closing the Strait of Hormuz, the waterway where about 40 per cent of all traded oil passes.