WASHINGTON - US President Barack Obama has imposed new sanctions on Iran’s central bank as he seeks to tighten a choke hold on the Islamic republic’s ailing economy and compel it to reverse course on its nuclear programme.Obama’s move, made public Monday, came as US officials warned foreign, non-American banks doing business with Tehran that they too could soon face sanctions, and amid speculation about a possible Israeli strike on Iran. The US president tried to still some of the nervousness at the weekend, saying that he did not think Israel had taken a decision to launch a high-risk military assault on underground nuclear plants it sees as an existential threat. But tightening a sanctions regime, he said, was already making Iran feel ‘unprecedented’ pressure. Officials revealed on Monday that Obama had signed an executive order the day before, implementing some new measures passed by Congress late last year.The sanctions block all property and interests of the Iranian government, the Central Bank of Iran (CBI) and all Iranian financial institutions that come within US jurisdiction. Previously, US institutions were required to reject, rather than block, such Iranian transactions.The exact dollar figure of assets involved was not immediately clear, but was likely small, with the new sanctions serving as a symbolic sign of US intent towards Tehran. Tough US and EU sanctions make it more difficult for Iran to pay for euro- and dollar-denominated goods, and for it to receive petro-dollars. But Tehran is now increasingly looking to Asia for commerce and trade opportunities.European sanctions on Iran are expected to have particular impact. The EU for instance imported some 600,000 barrels per day of Iranian oil in the first 10 months of last year - equivalent to nearly 20 per cent of Iran’s exports - making it the key market alongside India and China. But Europe last month banned all new contracts for Iranian oil.The measures passed last year also sought to deepen Iran’s financial isolation, giving Obama power to impose penalties on foreign financial institutions that do business with the CBI or other Iranian finance firms.Obama’s action on Monday however does not implement those sanctions, designed to bar Iran’s business partners from the lucrative US market. But the Treasury Department warned that firms doing business with Iran “remain at risk” of US punishments.Senior US officials are currently studying such punishments to find a way to implement them that maximizes pain for Iran, but does not spike oil prices, for instance, in a way that could harm the fragile US recovery.