A top legal adviser to the European Court of Justice issued an opinion Wednesday backing Iran's largest bank in a case against a German telecoms firm for tearing up a contract because of US sanctions. The advice from the advocate general said EU law prevents firms in the bloc from cutting ties with Iranian businesses in order to comply with sanctions reimposed on Tehran by former US leader Donald Trump. Iran's Bank Melli is suing Telekom Deutschland in Germany for ending a contract after it was placed on a US blacklist following Trump's decision to quit the 2015 nuclear deal. The argument centres on the EU's "blocking statute" designed to protect European companies from US extra-territorial sanctions targeting Iran and Cuba that seek to penalise firms for doing business with blacklisted entities. Bank Melli argued that the EU law -- which technically prohibits EU firms from complying with the US sanctions -- meant the German company could not end their contract. The advocate general backed that argument and said the German firm needed to show it had other reasons to terminate the contract beyond the US sanctions. Judges are set to give a definitive ruling on the arguments in the coming weeks. If the judges follow Wednesday's opinion, European firms fear it means they will end up being unable to avoid US sanctions as they would be forced to maintain contracts with sanctioned Iranian companies. The advocate general conceded that this left EU businesses "facing impossible -- and quite unfair -- dilemmas". The reach of US sanctions has long angered the EU and it has sought to protect its companies against punishment from Washington. Trump broke ranks with other world powers by pulling out of the Iran nuclear deal in 2018 and reimposing swingeing sanctions on Tehran. Delicate talks are currently under way in Vienna aimed at bringing the US back into the deal, a move that would see Washington lift many of the sanctions. del/rmb/lth