A Syrian fighter pilot has been granted asylum in Jordan after flying his plane to a military air base in the north of the country, officials say.
The defection of the MiG-21 pilot is the first involving the air force.
Syria has condemned the pilot as a traitor, and has asked the Jordanian government for the return of its plane.
Meanwhile ongoing violence has left 170 people dead, activists say, and the Red Cross has been unable to move civilians out of the restive city of Homs.
The Russian-made fighter landed at the King Hussein Air Base in Mafraq, close to the Syrian border, officials said.
The Syrian state news agency Sana named the pilot as Col Hassan Mirei al-Hamadeh, and said his plane was near the southern border when contact was lost early on Thursday.
A Jordanian security source said the pilot had flown from al-Dumair military airport, north-east of Damascus.
A Jordanian official told the Associated Press news agency that the pilot's request for asylum had been given on "humanitarian grounds" as the colonel would be tortured or killed if he returned home.
A spokesman for the rebel Free Syrian Army, Ahmad Kassem, said the group had encouraged the pilot to defect, AP reported.
The BBC's Jim Muir in Beirut says Col Hamadeh may well have flown over the Deraa area close to the southern border where some of the bloodiest fighting of the day has been reported.
According to activists, as many as 18 people died when the town of Inkhel in Deraa province was hit by shells and a series of raids by government forces.
The Syrian Observatory for Human Rights, a UK-based group, said nearly 170 people had been killed across Syria on Thursday - making it the deadliest day since April, when a ceasefire was due to come into force under an international peace plan.
The government says that 20 funerals have taken place for military personnel killed in earlier fighting.
More than 20 people were reported killed in the suburbs of Damascus.
A similar number of deaths was also reported in Homs, where the International Committee of the Red Cross (ICRC) has been unable to bring aid and medical supplies into the old city and take trapped civilians out.
Neither the reports of attacks nor the casualty figures can be independently verified.
Spokeswoman Carla Haddad Mardini told the BBC that the team in Homs had had to turn back "due to shooting and the security situation".
The ICRC team said it had been given assurances by government forces as well as opposition groups that there would be a two-hour pause in fighting in the worst affected areas.
Eventually, the team decided to abandon for the day its attempt to enter the old city and returned to Damascus.
In a separate development, the Russian government has confirmed for the first time that a cargo ship that was stopped off the north coast of Scotland and sent back to Russia was carrying three refurbished attack helicopters destined for Syria.
The MV Alaed had its insurance withdrawn because The Standard Club in London, which supplied its cover, said the ship had "broken internal rules".
UN observers have expressed fears recently about the use of such helicopters in attacks by government forces.
Last week, US Secretary of State Hillary Clinton accused Russia of escalating the conflict by supplying Syria with attack helicopters, although US officials later acknowledged the helicopters had been refurbished.
Russian Foreign Minister Sergei Lavrov said that reports that the ship was carrying helicopters that could be "used against peaceful demonstrators is quite a distortion aimed at whipping up passions and putting Russia in a bad light".
The BBC's defence and diplomatic correspondent, Jonathan Marcus, says Syria's air force has some three squadrons of Mi-25 Hind D attack helicopters, although it is not clear how many are operational.
Earlier this month, videos emerged on YouTube that appeared to show Mi-25s operating over the Syrian villages of Rastan and Farkia, near Idlib. If the videos are accurate, they would appear to be the first use of the Mi-25s in the current crisis, our correspondent says.
Mr Lavrov said the helicopters had been repaired by Russia under a 2008 contract.
He told Ekho Moskvy radio: "We are not breaching anything and we will perform our contractual obligations, which are not outside the restrictions imposed by the UN Security Council."