DUBAI/RIYADH, Sept 24 (Reuters) - Iranian flights to Gulf neighbours including travel hub Dubai appeared to have been cancelled on Thursday after a US deadline passed for global firms to halt work with Iran's airlines, a major step in a campaign President Donald Trump calls "economic D-Day".
In Saudi Arabia, where an escalating conflict with Yemen's Iran-aligned Houthi fighters this month has become the main front in the wider Middle East war, authorities said they had intercepted six ballistic missiles
fired by the Houthis.
With the US-Israeli war against Iran largely stalemated for months on the battlefield, Washington has announced a shift in tactics to extend the reach of its financial sanctions by targeting companies from third countries that do business with Iranian firms, a practice known as "secondary sanctions".
Trump referred to the new strategy last month as "economic D-Day", comparing it to the assault on Nazi-controlled France in World War Two by the United States and its allies.
The US Treasury had set September 23 as the deadline for companies worldwide to comply with an order to stop doing business with Iranian airlines. Washington says the aim is to ground the entire global Iranian civilian fleet.
Iran threatened on Wednesday to retaliate against any neighbouring countries that comply with the US ban on its flights, by making their airports "unusable".
There were no immediate public announcements from countries that they were halting flights, but Iran's ISNA news agency said all flights to the United Arab Emirates, the Gulf's biggest travel hub, had been halted as of midnight.
No arrivals or departures to Iran were visible on the website of Dubai or Abu Dhabi airports on Thursday. Websites of at least two Iranian airlines, Qeshm and Varesh, showed UAE flights had been cancelled. The UAE's General Civil Aviation Authority and Dubai Civil Aviation Authority did not respond to requests for comment.
The website of Iran's Imam Khomeini Airport in Tehran showed departures and arrivals on Thursday were still scheduled to and from countries including Afghanistan, Armenia, China, Iraq, Pakistan, Tajikistan and Turkey, but not nearby Gulf states. ISNA said a flight to Tajikistan had also been turned back because Turkmenistan had closed its airspace.
A flight ban, if sustained, could deepen Iran's isolation and worsen an economic crisis in the country, which is already facing a US blockade of its ports at sea.
"We are living in an open-air prison," a retired teacher in Tehran told Reuters by text message on condition her name not be used.
SAUDI ARABIA SAYS IT SHOOTS DOWN HOUTHI MISSILES
The war, which Trump launched alongside Israel in February as "Operation Epic Fury", has disrupted global energy supplies, killed thousands of people and pushed up oil prices.
It has reignited conflicts in other regional countries where Iran has allies, initially in Lebanon and now in Yemen, where the Houthis declared a blockade on Saudi Arabia in July and launched a lightning advance this month against a Saudi-backed government.
The Houthis have repeatedly fired into Saudi Arabia this month, and say the Saudi air force has conducted hundreds of strikes on Yemen since fighting escalated.
Saudi Arabia said it had intercepted six Houthi ballistic missiles on Thursday, after issuing emergency alerts for areas including the holy city of Mecca, Jeddah and Yanbu, the main Saudi Red Sea oil port.
"Any escalation and violations by the terrorist Houthi militia will be dealt with firmly," a Saudi-led coalition fighting the Houthis in Yemen said in a statement.
Sources in the internationally recognised, Saudi-backed Yemeni government said their forces had repelled overnight Houthi attacks on a key supply route to Aden, the Indian Ocean port city where the government is based.
The Houthis, who already controlled the north including the capital Sanaa, seized Yemen's entire Red Sea coast this month and have been pushing into adjacent highlands near the central mountain city of Taiz and road from Aden.
The Houthis have kept up pressure on government forces holding a steep winding mountain pass known as Hejat al-Abd, a lifeline for hemmed in pro-government forces, and for goods entering Taiz.
Seizing parts of the Taiz-Aden road could allow the Houthis to tighten their grip around Taiz and deal another blow to the government, which has struggled to regain the initiative since losing the western coast.
More than 700 people have been killed and thousands wounded in the latest fighting, according to the United Nations. Nearly 130,000 Yemenis have been displaced within the country, while more than 3,000 have fled by boat across the Red Sea to Africa.
(Reporting by Reuters bureaux, Writing by Peter Graff, Editing by Timothy Heritage)
