Qatar vowed on Thursday to ride out the isolation imposed on it by fellow Arab states over its alleged support for terrorism and said it would not compromise its sovereignty over foreign policy to resolve the region's biggest diplomatic crisis in years.

Saudi Arabia, the United Arab Emirates (UAE), Bahrain and Egypt severed relations with the small Gulf Arab state on Monday, accusing it of supporting Islamist militants and their arch-adversary Iran - charges Qatar calls baseless.

Several other countries later followed suit.

Would-be mediators including U.S. President Donald Trump and Kuwait's ruling emir have struggled to ease a crisis that Qataris say has led to a blockade of their nation.

Foreign Minister Sheikh Mohammed bin Abdulrahman al-Thani said Qatar had not yet been presented with a list of demands by countries that cut off diplomatic and transport ties, but insisted the matter be solved peacefully.

"We have been isolated because we are successful and progressive. We are a platform for peace," he told reporters in Doha in a defiant tone.

"We are not ready to surrender, and will never be ready to surrender, the independence of our foreign policy," he said, warning that the dispute threatened the stability of the region.

Saudi Arabia's closure of Qatar's only land border sparked fears of major price hikes and food shortages for its population of 2.7 million people, with long queues forming as some supermarkets began running out of stock.

With supply chains disrupted and anxiety mounting about deepening economic turbulence, banks and firms in Gulf Arab states were trying to keep business links to Qatar open and avoid a costly firesale of assets.

"We're not worried about a food shortage, we're fine. We can live forever like this, we are well prepared," Sheikh Mohammed said.

He said Iran was ready to help with securing food supplies in the emirate, an investment powerhouse and supplier of natural gas to world markets but tiny and reliant on imports.

Turkey has meanwhile brought forward a planned troop deployment to Qatar and pledged to provide food and water supplies to its Arab ally, which hosts a Turkish military base.

A senior UAE official accused Qatar of escalating the row by seeking help from Turkey and Iran.

"The request for political protection from two non-Arab countries and military protection from one of them could be a new tragic and comic chapter," UAE Minister of State for Foreign Affairs, Anwar Gargash, wrote on Twitter.

MEDIATION EFFORTS FALTER

Trump initially took sides with the Saudi-led group before apparently being nudged into a more even-handed approach when U.S. defence officials renewed praise of Doha, mindful of the major U.S. military base hosted by Qatar that serves, in part, as a launchpad for strikes on Islamic State insurgents.

In his second intervention in as many days, Trump urged action against terrorism in a call with Qatari Emir Sheikh Tamim bin Hamad al-Thani on Wednesday and offered help in resolving the crisis, including through a meeting at the White House.

But a Qatari official said on Thursday the emir would not be accepting the invitation.

"The emir has no plans to leave Qatar while the country is under a blockade," the official told Reuters.

The White House said Trump was continuing to talk with all partners. U.N. Secretary-General Antonio Guterres was also ready to support diplomatic efforts "if desired by all parties," his spokesman said.

Saudi Foreign Minister Adel al-Jubeir, who has said Gulf states could resolve the dispute among themselves without outside help, travelled to Muscat on Thursday to meet his Omani counterpart.

But there have been few signs of progress as officials from Qatar and its Arab neighbours in the Gulf Cooperation Council (GCC) pursue shuttle diplomacy.

"The feeling here is that it is going to take a while to fix. It is more about preventing things from getting worse," said one diplomat in Kuwait, whose leader was in both the UAE and Qatar on Wednesday for consultations.

"IT IS A BLOCKADE!"

The UAE's national postal group suspended services to Qatar and the UAE aviation authority said it had closed air space for traffic to and from Doha.

The Abu Dhabi Petroleum Ports Authority also reimposed a ban on oil tankers linked to Qatar calling at ports in the UAE, reversing a decision to ease restrictions and potentially creating a logjam of crude cargoes.

"It is a blockade! Like that of Berlin. A declaration of war. A political, economic and social aggression," a Qatari diplomat said. "We need the world to condemn the aggressors."

Authorities tried to calm nerves on Wednesday, releasing a video showing a shop with shelves brimming with food and reassuring Qataris - the wealthiest people in the world per capita - that their quality of life would not be hit.

The International Monetary Fund said it was too early to assess the economic impact. But in a sign of the damage, Standard & Poor's downgraded Qatar's debt on Wednesday as its riyal currency fell to an 11-year low.

AL JAZEERA CAUGHT IN ROW

Qatar has backed Islamist movements but strongly denies supporting terrorism. It provides a haven to anti-Western groups like the Afghan Taliban, Palestinian Hamas and Algeria’s Islamic Salvation Front but says it does not accept its neighbours' view that any group with an Islamist background is terrorist.

Egypt on Thursday called for the United Nations Security Council to launch an investigation into accusations, denied by Qatar, that it paid a ransom of up to $1 billion to "a terrorist group active in Iraq" to release kidnapped members of its royal family.

In an interview with BBC radio, UAE Ambassador to Russia Omar Saif Ghobash said Qatar had to choose between supporting extremism or supporting its neighbours.

"Qatar needs to decide: Do you want to be in the pocket of Turkey, Iran and Islamic extremists? They need to make a decision; they can't have it both ways," he said.

The Saudi newspaper al Watan published what it called a list of eight "extremist organisations" seen as working to destabilise the region from Qatar, including Qatar's Al Jazeera news channel, that were targeted by Gulf Arab states.

State-funded Al Jazeera's acting director general, Mostefa Souag, dismissed accusations that its reportage is pro-Islamist and amounts to meddling in the affairs of other Arab states. "We don't interfere in anybody’s business, we just report," he told Reuters at Al Jazeera's Doha headquarters.

A company source later said the network was combatting a large-scale cyber attack but remained operational, and Qatar's official state TV said it had shut down its website temporarily after facing hacking attempts.

Qatar said last month its state news agency had been hacked and false statements attributed to its ruler posted, helping ignite this week's rift with other Arab states.