Pakistan, Aug. 28 -- The prime minister of US ally Qatar visited Tehran on Thursday in a bid to revive diplomacy as the US and Iran traded recriminations over Washington's latest sanctions drive, described by one Iranian official as "all-out economic war".

A Gulf neighbour of Iran, 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. The visit comes as the war nears its sixth month with fighting largely paused but no diplomatic breakthrough in sight. Both sides are at odds over control of the Strait of Hormuz, a chokepoint for global oil supplies that Tehran has used as leverage.

The White House said there were currentl...