Thirty-six people have been killed by security forces in Syria, activists say, as the deadline expired for the government to agree on a new Arab League plan to allow observers in to monitor the country's unrest or face further sanctions.
Syria signalled on Sunday that it might still be willing to comply with the Arab League's plan but was negotiating some details.
"Messages are being exchanged between Syria and the Arab League to reach a certain vision that would facilitate the mission of observers in Syria, while preserving Syrian interests and sovereignty," Foreign Ministry spokesman Jihad Makdissi said in Damascus.
Asked later in the day whether any decision had been made, he said: "If there are good intentions, the road is open toward signing an agreement." A more detailed response would be made on Monday, he said.
AFP news agency quoted a senior Qatari official as saying Damascus had asked for "new clarifications and further amendments to be made to the protocol which was proposed" to cover the deployment of the observer mission.
But the Arab ministers had "refused".
The Qatari official said, however, that if Syrian officials "still want to sign; they can come tomorrow to Cairo."
Syria's failure to meet an earlier deadline on November 25 to allow observers saw the imposition of a raft of measures aimed at halting the authorities' violent crackdown on dissent. Measures including a ban on dealings with the country's central bank and a freeze of Syrian government assets have already been imposed.
Arab ministers have continued to meet to work out enforcement of the existing sanctions package.
Turkey also imposed sanctions on Syria last week, including a freeze on government assets and suspension of all financial dealings with Syria.
The state-run SANA news agency reported on Sunday that the Syrian government had decided to retaliate by suspending a free trade agreement which allows Turkish imports into Syria tax-free and by introducing a 30 per cent tariff on all Turkish goods.
Jordan 'seeks exception'
Meanwhile, Al Jazeera's Nisreen El-Shamayleh, reporting from neighbouring Jordan, said she was hearing that the Jordanian government was asking the Arab League to be excluded from imposing sanctions because of the economic losses involved.
"Jordan is concerned about stopping flights between Damascus and Amman and about a high volume of trade between the two countries, amounting to $400 million per year", she said.
"Nonetheless, Jordan says that as a government it supports the Arab consensus on punitive measures but it does not want to cut its bilateral economic ties."
Iraq and Lebanon have already said they will not impose sanctions on their neighbour.
US Assistant Secretary of State Jeffrey Feltman said monitors were needed to keep a check on the forces of Syrian President Bashar al-Assad.
In-depth coverage of escalating violence across Syria
"We believe that in full light of monitors and media, the security services reporting to Assad and his clique would not be able to operate the way they are operating now," he said in Jordan.
Allowing in monitors would be a "peaceful way of trying to stop this sustained cycle of violence that Assad seems committed to turning Syria into," Feltman said.
He accused Assad of forcing his minority Alawite sect, which has a tight grip on the country's military and security apparatus, into a bloody conflict with the country's majority Sunnis.
"Bashar al-Assad is the one who is deepening the sectarian hatred. He seems to be intent on fulfilling his own prophecy that Syria is going to move into chaos and civil war,"
Feltman said Washington has been in touch with Syrian Christians to prod them "not to stand on the side of the attacker," but declined to elaborate.
Many among Syria's Christian and other minorities have sided with Assad, fearing they would be targeted if the Sunni majority takes over.
Authorities blame Sunni "extremists" and a foreign-backed conspiracy for the violence and the killing of more than 1,100 soldiers and police.
Meanwhile, activists say November was the bloodiest month since the uprising started in March, with more than 700 civilians killed.
A majority of Sunday's deaths were reported in Homs province, which has become a focal point of the country's unrest.
The United Nations' top human rights forum on Friday condemned Syria for "gross and systematic" violations by security forces, including executions and the imprisonment of about 14,000 people.
Syria dismissed the UN vote as "unjust" and "prepared in advance by parties hostile to Syria" in a foreign ministry statement carried by SANA.
More than 4,000 people have died since protests broke out in March, according to the United Nations, which says the violence in Syria is taking the shape of a civil war.
Most foreign media have been banned from Syria, making it difficult to verify reports.