Qatar hit back Friday at a threat by four "siege countries" to impose further sanctions on the emirate over its refusal to bow to their ultimatum for ending the Gulf crisis.

In a statement attributed to a senior foreign ministry source, a defiant Qatar said the demands of Saudi Arabia, Egypt, the United Arab Emirates and Bahrain were defamatory.

"The State of Qatar expressed regret over the content of the two statements issued in Cairo and Jeddah by the four siege countries and the false accusations included in them that amount to defamation in contradiction with the established foundations of international relations," read the statement.

"A senior Foreign Ministry source described the statements' claims about the State of Qatar's interference in internal affairs of countries and financing terrorism as baseless allegations."

Earlier on Friday, Saudi Arabia and its three allies said Qatar's rejection of a list of 13 demands they set to lift sanctions on Doha "reflects its intention to continue its policy, aimed at destabilising security in the region," according to a statement on the official SPA news agency.

"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 added, without elaborating.

It is the latest impasse in the worst diplomatic crisis in the Gulf for several years, which has now stretched into its second month.

In June, the four states announced the severing of all diplomatic ties with Qatar over allegations the emirate bankrolled Islamist extremists and had close ties with Saudi Arabia's arch-rival Iran.

Then, on June 22, they issued a list of demands, including the shutdown of broadcaster Al-Jazeera in order to lift the sanctions.

Qatar, which denies being a supporter of extremism, rejects the "unrealistic" demands as an attempt by the Gulf states to undermine the nation's sovereignty.

Source: AFP