WASHINGTON/CAIRO, April 3 -- Hopes for a swift end to the Middle East war faded on Thursday after US President Donald Trump vowed more aggressive strikes on Iran, sending oil prices sharply up again in a blow to consumers around the world. Stocks slid and the dollar gained after Trump said military operations would be intensified without offering the timeline that investors had sought for ending hostilities against Iran. "We're going to hit them extremely hard over the next two to three weeks. We're going to bring them back to the Stone Ages where they belong," Trump said in a Wednesday evening prime-time speech. Trump said the US would achieve its military objectives soon but suggested the war could escalate if Iranian leaders did not give in to Washington's terms during negotiations, with strikes on Iran's energy and oil infrastructure possible. He has said he may end the war with a deal and told countries that rely on fuel shipments through the Strait of Hormuz, which has been all but closed by Iranian attacks, to "just grab it". European and other states have said they will only help secure the strait if there is a ceasefire. With pressure growing, some 40 countries were exploring ways to restore freedom of navigation at virtual talks on Thursday. "It can only be done in consultation with Iran," French President Emmanuel Macron said during a visit to South Korea. Iran's armed forces responded to Trump with a warning for the United States and Israel of "more crushing, broader and more destructive" attacks in store. The war will continue until the "permanent regret and surrender" of Iran's enemies, said Ebrahim Zolfaqari spokesperson for the Iranian military's Khatam al-Anbiya central headquarters, in a statement carried by Iranian media. Fears are growing that the conflict may leave Iran with a stranglehold over Middle East energy supplies now that it has shown that it can block the vital Strait of Hormuz by targeting oil tankers and attacking Gulf countries hosting US troops. Gulf states say they reserve the right to self-defence but have not responded militarily to repeated attacks by Iran over the past month to avoid escalation into a far more devastating all-out Middle East war. Iran's parliament was reviewing a bill that would formalise the blocking of vessels from hostile countries passing through the strait and the charging of tolls for others wishing to pass, spokesperson Abbas Goodarzi said. Thousands of people have been killed across the Middle East since February 28, when the US and Israel began air strikes on Iran, triggering Iranian attacks on Israel, US bases and the Gulf states, while opening a new front in Lebanon....