A top US diplomat underlined Washington\'s opposition to a French-backed plan which, if realised, would see a pipeline built from Kazakhstan to Iran to export the massive oil reserves underneath the Caspian Sea. \"The US is firmly opposed to this pipeline, for reasons both of law and policy,\" Steven Mann, the US special envoy on Caspian basin energy issues, told reporters. \"Commercially speaking, I think there are better alternatives,\" added Mann, who was speaking on the sidelines of the annual Caspian Oil and Gas conference in Azerbaijan\'s capital, Baku. Kazakhstan\'s government, together with French oil major Total, has been studying the feasibility of building a pipeline to ship crude from Kazakhstan to Iran, and from there to tanker terminals on the Persian Gulf. However, the idea has angered Washington. It has indentified Iran as part of an \"axis of evil\" and has banned US companies from doing business with Iran\'s clerical regime. The Caspian Sea -- and especially Kazakhstan\'s sector -- is home to some of the world\'s largest untapped oil reserves. It is estimated that there are up to 33 billion barrels of crude under the seabed, which is twice the size of the reserves in the North Sea. The landlocked Caspian has attracted the attention of investors who want to diversify oil supplies away from the Middle East, which, they say, is vulnerable to political instability. Washington has backed the construction of the Baku-Tbilisi-Ceyhan pipeline, which will export Caspian oil west across Azerbaijan, Georgia and Turkey, to the Mediterranean Sea. That project is due to be completed by the middle of next year. However, some in the oil industry say the southern route, through Iran, is shorter and commercially more attractive. (AFP)