The American State Department says it has revoked the Visa of the Venezuelan Ambassador to the United States. It follows the refusal of President Hugo Chavez to accept the proposed US Envoy to Caracas. The move comes amid a diplomatic dispute between the two countries over President Barack Obama's choice of ambassador to Caracas, Larry Palmer. Venezuelan President Hugo Chavez had been angered by comments Mr Palmer made about the country this year. Washington's move effectively expels Venezuela's envoy, Bernardo Alvarez Herrera. It is not thought that Mr Herrera is currently in the US but the revocation means he cannot return.