Qatar's foreign minister said Doha was ready to discuss "legitimate issues" with Arab states to end the regional crisis, but some demands made by the Gulf countries were impossible to meet.
Qatar said on Thursday it was working with the United States and Kuwait to respond to a list of demands presented by Arab states who have accused Doha of supporting terrorism.
The feud erupted this month when Saudi Arabia, the United Arab Emirates, Bahrain and Egypt severed diplomatic and travel links with Qatar, accusing it also of courting regional foe Iran. Qatar denies the allegations.
The four countries have sent Doha a list of 13 demands, including closing the state-funded Al Jazeera television station and reducing ties to Iran, an official of one of the four countries said. They gave Doha 10 days to comply.
The deadline is expected to expire on Sunday. Kuwait, which retained ties with Qatar, is trying to mediate in the dispute with the support of Washington.
"Regarding the ten days deadline, we are working together with the Americans and the Kuwaitis in order to prepare the proper (responses) ... to the list which has been submitted to us," Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman Al Thani told reporters in Washington.
"The negotiation should be under the right conditions. We have to set the conditions first in order to pursue these negotiations," Sheikh Mohammed said.
Al Jazeera also quoted him as saying that the setting of a deadline by the four countries impinged on Qatar's sovereignty and as calling the demands "unreasonable".
Earlier, he said in a statement that Doha was ready to discuss "legitimate issues" with Arab states to end a regional crisis, but that the list contained some demands impossible to meet because the underlying accusation was untrue.
"We cannot 'sever links with so-called Islamic State, Al Qaeda and Lebanese Shia militant group Hezbollah' because no such links exist," he said in a statement. "And we cannot 'expel any members of Iran's Revolutionary Guard' because there are none in Qatar."
Complaint to WTO
Qatar said it was considering launching a complaint at the World Trade Organisation against the blockade.
"We work under the premise that these measures are going to be in place for a while. It's not necessarily so, but we have to work under this premise," Ali Alwaleed al-Thani, director of Qatar's WTO office said.
The UAE ambassador to Russia has said Qatar could face fresh sanctions if it does not comply with the demands. The Gulf states could ask their trading partners to choose between working with them or Doha, he said in a newspaper interview.
Sheikh Mohammed said in the statement that since it was impossible for Doha to stop doing things it had never been doing, "we are left to conclude that the purpose of the ultimatum was not to address the issues listed, but to pressure Qatar to surrender its sovereignty.
"This is something we will not do."
In Washington, he said the demands were "meant to be rejected" and that they informed Secretary of State Rex Tillerson that the demands were "unrealistic."
NATO ally Turkey has backed Doha in the rift. Qatar's defence minister is due to visit Ankara on Friday and will hold talks with his Turkish counterpart, sources at Turkey's defence ministry said.