Qatar has accused Saudi Arabia, Bahrain, the United Arab Emirates and Egypt of “clear aggression” against the Gulf state.
It comes as ministers from the latter four nations said Qatar’s undisclosed response to their 13 demands was “not serious”.
Those demands were in exchange for ending the sanctions they imposed on the gas-rich country a month ago, accusing it of backing terrorism in the region.
They also cut diplomatic and transport links with the country.
The 13 demands included wanting Qatar to curtail its support for the Muslim Brotherhood, shut down the al Jazeera TV channel, close a Turkish military base and downgrade its ties with regional rival Iran.
At a news conference in Cairo, Egyptian foreign minister Sameh Shukri said Qatar’s response was “generally negative” and did not “lay the foundation for Qatar’s reversal of the policies it pursues”.
Qatar says the Gulf states’ demands were so tough that they suspect they were never seriously meant to be negotiated. The country also denies any involvement in terrorism.
Speaking in London, Qatari foreign minister Sheikh Mohammed bin Abdulrahman al-Thani, said the charges “were clearly designed to create anti-Qatar sentiment in the west”.
He claimed shipping costs were now 10 times higher and it planned to raise liquified natural gas (LNG) production capacity by 30% in the next five years.
President Trump has urged a resolution to the crisis as he spoke to Egyptian president Abdel Fattah al-Sisi on the phone.
The US leader reiterated the need for all countries “to stop terrorist financing and discredit extremist ideology”, said the White House.
Qatar has invested heavily in infrastructure projects in western countries and owns a large amount of property in London.
It also has close diplomatic ties with the US over the Syria war.
Mr al-Thani said: “Reading between the lines, the blockading countries were demanding that we have to surrender our sovereignty to end the siege, something which… Qatar will never do.”
He continued: “Qatar continues to call for dialogue despite the violation of international laws and regulations, despite the separation of 12,000 families, despite the siege that is a clear aggression and an insult to all international treaties, bodies and jurisdictions.”
Qatar faces possible expulsion from the Gulf Cooperation Council (GCC), a regional economic and security body founded in 1981, if its response to the demands fails to satisfy the Arab states.
Meanwhile, there are claims Saudi Arabia is “undoubtedly at the top of the list” when it comes to funding Islamist extremism in Britain.
The Henry Jackson Society said a clear and growing link can be drawn between overseas money, which mainly comes from Saudi Arabia, and the recent wave of attacks in the UK and Europe.
But Saudi Arabia’s UK embassy has labelled the claim “categorically false”.