Qatar has expressed regret over false claims in statements issued by Saudi Arabia and its allies in Cairo and Jeddah, describing the accusations by the anti-Doha quartet as defamation.

Qatar's state news agency quoted a foreign ministry source as saying on Friday that the claims by Saudi Arabia, the United Arab Emirates, Bahrain and Egypt about Qatar's interference in internal affairs of other countries and financing terrorism are baseless allegations.

Qatar's position of rejecting and condemning all forms of terrorism is consistent and known, the source said, adding:

"The State of Qatar is an active member committed to combating terrorism and its financing at regional and international levels. The international community attests to that."

Qatar remains ready to "cooperate and review all claims that do not contradict the sovereignty of the State of Qatar," the source continued.

The source also criticised the anti-Qatar group for accusing Doha of leaking the list of demands, saying the claims were baseless and could be refuted with evidence.

In a joint statement released late on Thursday, Saudi Arabia and its allies said that Qatar's refusal of their list of 13 demands was proof of its links to terror groups and threatened to impose further sanctions on Doha over its refusal to bow to their ultimatum for ending the Gulf crisis.

READ MORE - All the latest updates about the Gulf crisis

"All political, economic and legal measures will be taken in the manner and at the time deemed appropriate to preserve the four countries' rights, security and stability," the statement said.

A similar document was issued on Wednesday after the foreign ministers of the quartet met in the Egyptian capital Cairo.

Crisis 'could intensify'

Saudi Arabia, the UAE, Bahrain and Egypt cut ties with Qatar on June 5 and imposed a land, air and sea blockade on the country.

They also ordered Qatari citizens to leave their territories and took various steps against Qatari firms and financial institutions.

On June 22, they issued a 13-point list of demands, including the shutdown of Al Jazeera, as a prerequisite to lift the sanctions. The quartet now considers the demands "null and void".

The US state department warned on Thursday that the Gulf crisis is at an impasse and could potentially drag on for weeks or even months.

The US believes the crisis could "possibly even intensify", Heather Nauert, a spokesperson for the state department, said.

Nauert did not specify what type of escalation the US fears, but she said Secretary of State Rex Tillerson remains in close contact with the countries involved.