Qatar PM visits Tehran to pursue mediation efforts

By Yomna Ehab and Parisa Hafezi CAIRO/DUBAI, Aug 27 (Reuters) - Qatar's prime minister visited Tehran on Thursday in a bid to relaunch diplomacy after the U.S. and Iran traded recriminations over Washington's promise to increase economic pressure, a move one Iranian official described as "all-out economic war". A Gulf neighbour of Iran and a U.S. ally, Qatar has served as a back-channel negotiator for the warring parties and played a direct role in securing a June ceasefire that briefly led to a cessation of hostilities.