Iranian police have warned they are ready to use force to prevent a rally in the capital Tehran over the disputed presidential poll. Hundreds of police are said to have gathered in the city centre, amid an atmosphere of extreme tension. There are conflicting reports as to whether the rally will go ahead. But correspondents say a demand by the country’s supreme leader to end street protests appears to have made some protesters merely more determined. People contacting the BBC from Tehran spoke of a heavy security presence in the area around Enghelab Square. Users of the micro-blogging site Twitter said protesters were gathering.