The United Nations has reached a deal with Syria outlining the rules for the deployment of observers to monitor the country's ceasefire, both sides said.
A spokesman for UN-Arab League envoy Kofi Annan said the agreement covered the functions of the mission and the Syrian government's responsibilities.
A nominal truce is in place in Syria, but reports of violence have continued.
Meanwhile, the UN's chief Ban Ki-moon is due to brief the Security Council on the situation in New York.
Earlier, Mr Ban said violence had escalated in recent days, and said he wanted the observer mission to increase to 300, to be deployed over three months.
Some correspondents say the Security Council, which is not due to make a decision until next week, may be afraid to put unarmed observers on the ground if the situation continues to deteriorate at the same rate.
It is also not clear how freely observers will be permitted to move around under the terms agreed with the Syrian authorities.
The Syrian Observatory of Human Rights, an activist group, said fresh fighting on Thursday killed at least three people across the country.
There has also been further government shelling of parts of the third-biggest city, Homs, the BBC's Jim Muir reports from neighbouring Lebanon.
Deputy Foreign Minister Faisal al-Mekdad and a member of the advance team, which arrived in the country earlier this week, signed the preliminary accord in Damascus, the Syrian foreign ministry said.
"This agreement comes within the framework of Syrian efforts aimed at making the Annan plan succeed and to facilitate the UN observer mission while respecting Syria's sovereignty," a statement said.
The office of Mr Annan confirmed an agreement had been signed, and said it was also having discussions with representatives of Syrian opposition groups.
"This agreement outlines the functions of the observers as they fulfil their mandate in Syria and the tasks and responsibilities of the Syrian government in this regard," Ahmad Fawzi said in a statement.
In a report to the UN, Mr Ban said the Syrian government had not complied with the terms of the peace deal, but that there remained an "opportunity for progress".
While violence had fallen at the time of the truce on 12 April, it had escalated again in recent days, he said. Mr Ban said it was critical that the government kept its pledge to withdraw troops from populated areas.
He also noted that there had been "no significant release of detainees", and "no substantive progress" in negotiations on humanitarian access, in reference to other aspects of Mr Annan's six-point plan.
He said observers had been prevented from going to the city of Homs after the government cited "security concerns". But observers were allowed to visit the town of Deraa freely.
Our correspondent says that while the trip to Deraa took place without incident, observers found themselves mobbed by protesters in the Damascus suburb of Arbeen.
Gunfire broke out and observers had to get out, he says. Several demonstrators were injured, according to activists.
In his report, Mr Ban said: "The situation in Arbeen became tense when a crowd that was part of an opposition demonstration forced United Nations vehicles to a checkpoint."
"Subsequently, the crowd was dispersed by firing projectiles. Those responsible for the firing could not be ascertained by the United Nations military observers."
Meanwhile, US Secretary of State Hillary Clinton is taking part in a Friends of Syria meeting of foreign ministers in Paris to discuss the crisis.
Ahead of the meeting, President Sarkozy of France accused the regime of trying to wipe out Homs altogether, and called for the imposition of humanitarian corridors.
Also on Thursday, Britain announced that it was contributing £4m ($6.4) to a UN fund for humanitarian needs caused by the conflict, on top of more than £4m it has already disbursed.