European Union leaders agreed tighter sanctions against Iran Thursday, including measures to block investment in the oil and gas sector and curtail refining and natural gas capability. The EU sanctions follow the US Treasury's decision Wednesday to impose new sanctions on Iran to curb its nuclear program, blacklisting another of its state-controlled banks, companies that are fronts for its state shipping line, and more of its Revolutionary Guard Corps. The Treasury also took a separate step to squeeze Iran's energy sector by identifying some 20 petroleum and petrochemical companies as being under Iranian government control. They also identified two insurance companies that would fall under the trade embargo, including one based in Britain. The EU measures go substantially beyond the sanctions the United Nations agreed on June 10 and are designed to pressure Tehran to return to talks over an uranium enrichment programme Western powers believe is designed to produce nuclear weapons. The steps, which could come into force within weeks, will focus on trade, including dual-use items, banking and insurance, Iran's transport sector, including shipping and air cargo, and key sectors of the gas and oil industry. The energy sector sanctions will prohibit “new investment, technical assistance and transfers of technologies, equipment and services related to these areas, in particular related to refining, liquefaction and Liquefied Natural Gas technology”, the heads of state and government said in their conclusions.