A spokesman for UN envoy Kofi Annan said Syria has accepted his plan to end the violence that has racked the country for a year.
Annan's plan calls for a ceasefire by Syrian forces, a daily two-hour halt to fighting to evacuate injured people and provide humanitarian aid, and inclusive talks about a political solution.
Ahmad Fawzi, Annan's spokesman, said the Syrian government's acceptance of the proposal was made by letter, AP reported.
Annan is in Beijing to rally support for stopping the bloodshed.
Syrian opposition groups had criticised the plan for not calling on Assad to step down.
News that Syria has accepted the plan came as civilians in Lebanon claimed Syrian army troops had crossed the border and attacked homes where they believed Free Syrian Army rebels were hiding.
"More than 35 Syrian soldiers came across the border and started to destroy houses," Abu Ahmed, 63, a resident of al-Qaa told Reuters.
Other residents said the army had used "armoured personnel vehicles, fired rocket-propelled grenades and exchanged heavy machinegun fire with rebels", the report added.
It also emerged that Syrian authorities have banned men aged between 18 and 42 from travelling abroad unless they serve their compulsory military draft, opposition sources and activists said.
The UN said that more than 8,000 people have been killed in Syria's year-long uprising.