AFP - Shiite rebels in Yemen threatened on Tuesday to attack ports and airports in Saudi Arabia and the United Arab Emirates, raising the stakes in a flare-up between Riyadh and Tehran.
The threat came hours after Saudi Arabia's powerful crown prince accused Iran of "direct military aggression" through its support for the rebels -- a claim Tehran rejected as "contrary to reality".
The soaring tensions between the key oil producers saw crude trading at close to two-year highs on Tuesday and spooked Gulf markets.
The rebels already showed on Saturday that despite a more than two-year Saudi-led bombing campaign, they retain missiles capable of striking targets deep inside the kingdom.
A rebel missile was intercepted and destroyed near Riyadh international airport -- the first to reach the Saudi capital -- with smouldering debris inside the perimeter underscoring the growing fallout for Saudi Arabia from its involvement in neighbouring Yemen.
"All airports, ports, border crossings and areas of any importance to Saudi Arabia and the UAE will be a direct target of our weapons, which is a legitimate right," the rebels' political office said in statement.
"We will not stand idly by -- we will seek more radical means to prevent both the tightening of the blockade and all acts aimed at starving and humiliating the people of Yemen."
Saudi Arabia and the UAE are the two major powers in a coalition that has been fighting against the Yemeni rebels since 2015 in support of the internationally recognized government.
Since Saturday's missile attack, the coalition has tightened its blockade of rebel-held areas of Yemen, blocking even UN-supervised relief supplies despite urgent appeals from the world body.
The coalition said its action was aimed at filling the gaps in inspection procedures that enable "smuggling of missiles and military equipment" to the rebels.
But the blocking of all relief supplies further threatens some seven million people already on the brink of famine and the UN urged the coalition to lift it as soon as possible.
"If these channels, these lifelines, are not kept open it is catastrophic for people who are already in what we have already called the world's worst humanitarian crisis," said Jens Laerke, a spokesman for the UN humanitarian office (OCHA) in Geneva.
Saturday's missile attack sparked a bitter war of words between Sunni-ruled Saudi Arabia and predominantly Shiite Iran.
"The involvement of Iran in supplying missiles to the Houthis is a direct military aggression by the Iranian regime," the official Saudi Press Agency quoted Crown Prince Mohammed bin Salman as saying.
This "could be considered an act of war," he said.
Iranian Foreign Minister Mohammad Javad Zarif retorted that "the allegations by Saudi officials were contrary to reality", a foreign ministry spokesman said.
The rebels' threat of more missile attacks like that on Riyadh airport threatens to escalate the proxy conflict between Riyadh and Tehran, which back opposing sides in wars and power struggles from Yemen to Syria.
On Monday, the Saudi-led military coalition in Yemen said it reserved the "right to respond" to the missile attack, calling it a blatant military aggression by the Iranian regime which might amount to an act of war.
Six Gulf Arab bourses ended lower on the tensions and the Saudi market was down 2.9 percent in afternoon trade at levels last seen more than five months ago.