PHUKET, Thailand, (Reuters/AFP) - US Secretary of State Hillary Clinton signed a friendship treaty with Southeast Asia on Wednesday, underlining Washingtons renewed focus on a region that has increasingly come under Chinas influence. Other countries including China have acceded to the Treaty on Amity and Cooperation, a document that underpins the 10-member Association of South East Asian Nations (ASEAN). It commits signatories to the peaceful settlement of disputes and non-interference in domestic affairs. The U is back in Southeast Asia, Hillary declared at a news conference on the Thai island of Phuket before she signed the treaty and held talks with ASEAN foreign ministers. Earlier, Hillary said the US is ready to help its Gulf allies establish a defence umbrella if Iran does not back down over its nuclear programme, Secretary of State Hillary Clinton said Wednesday. Clinton told Thai television that the administration of President Barack Obama was still open to engagement with Iran over its atomic drive but said that if Tehran obtains the bomb, then it would not make it any safer. We will still hold the door open. But we also have made it clear that we will take action, as Ive said time and time again, crippling action, working to upgrade the defence of our partners in the region, she said. If the US extends a defence umbrella over the region, if we do even more to support the military capacity of those in the Gulf, it is unlikely Iran will be any stronger or safer, Clinton said. They wont be able to intimidate and dominate as they apparently believe they can once they have a nuclear weapon.