A Gulf official said that Qatari Foreign Abdulrahman Al-Thani had delivered it during a short visit to Kuwait.
Kuwait City: Qatar on Monday responded to a list of demands from Saudi Arabia and its allies after they agreed to give a defiant Doha another 48 hours to address their grievances.
Details of the response were not immediately available, but a Gulf official said that Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman Al-Thani had delivered it during a short visit to Kuwait, which is acting as a mediator in the crisis.
Saudi Arabia, the United Arab Emirates, Bahrain and Egypt had announced in the early hours of Monday they were pushing back a deadline for Qatar to agree to a list of 13 demands they issued on June 22.
A joint statement said they were extending the ultimatum, which had been due to expire at the end of the day on Sunday, at the request of Kuwait's emir.
The demands included Doha ending support for the Muslim Brotherhood, closing broadcaster Al-Jazeera, downgrading diplomatic ties with Iran and shutting down a Turkish military base in the emirate.
Sheikh Mohammed had earlier said the list of demands was "made to be rejected" and on Monday British lawyers for Qatar denounced the demands as "an affront to international law".
"They are reminiscent of the extreme and punitive conduct of 'bully' states that have historically resulted in war," the lawyers said in a statement.
Saudi Arabia and its allies announced on June 5 they were severing ties with their Gulf neighbour, sparking the worst diplomatic crisis to hit the region in decades.
They accused Qatar of supporting extremism and of being too close to Saudi Arabia's regional arch-rival Iran, which Doha has strongly denied.
The crisis has raised concerns of growing instability in the region, home to some of the world's largest energy exporters and several key Western allies who host US military bases.
German Foreign Minister Sigmar Gabriel, who on Monday starts a tour of several Gulf states, called for "serious dialogue" to end the crisis.
"We are worried that the distrust and the disunity could weaken all the parties concerned as well as the entire peninsula," said Gabriel, who will visit Saudi Arabia, the United Arab Emirates and Qatar.
Riyadh and its supporters have already severed air, sea and ground links with Qatar, cutting off vital routes for imports including food.
They also ordered Qatari citizens to leave their territories and took various steps against Qatari firms and financial institutions.
It is unclear what further measures will be taken if Qatar fails to meet the demands, but the UAE's ambassador to Russia Omar Ghobash warned last week that further sanctions could be imposed.
As well as taking steps to expel Qatar from the six-member Gulf Cooperation Council, Riyadh and its allies could tell their economic partners to choose between business with them or with Doha, he told Britain's Guardian newspaper.
Qatar has long pursued a more independent foreign policy than many of its neighbours, who tend to follow the lead of regional powerhouse Saudi Arabia.
Doha has said it is ready for talks to end the crisis. Kuwait, which unlike most of its GCC neighbours has not cut ties with Qatar, has been heading up mediation efforts.
US Secretary of State Rex Tillerson has also called for compromise and hosted senior Gulf officials, but his efforts have been undermined by remarks from President Donald Trump apparently supporting Riyadh's position.
Trump spoke separately on Sunday with the Saudi king, Abu Dhabi's crown prince and the Qatari emir on his concerns over the dispute, the White House said.
Trump "underscored that unity in the region is critical," the statement said, but also "reiterated the importance of stopping terrorist financing and discrediting extremist ideology."
Egypt said it would host the foreign ministers of Saudi Arabia, the United Arab Emirates and Bahrain on Wednesday to discuss the crisis.
The German government also announced that Saudi Arabia's King Salman had cancelled plans to attend this week's G20 summit in Hamburg.