LONDON - Iran's announcement that it will abandon limitations on enriching uranium is extremely concerning and Britain is urgently speaking to parties about possible next steps, a spokesman for Prime Minister Boris Johnson said on Monday.The spokesman also said there were international conventions in place to prevent the destruction of cultural heritage after U.S. President Donald Trump threatened to hit 52 Iranian sites, including targets important to Iranian culture, if Tehran attacks Americans or U.S. assets."Iran's announcement is clearly extremely concerning. It is in everyone's interests that the deal remains in place. It makes the world safer by taking the prospect of a nuclear-armed Iran firmly off the table," the spokesman told reporters."We have always said the nuclear deal is a reciprocal deal, and in light of Iran's announcement we are urgently speaking to partners about next steps."On Trump's threat to strike Iranian sites, the spokesman said: "There are international conventions in place which prevent the destruction of cultural heritage."