BEIRUT -- Syrian government troops on Thursday flushed out rebels who had stormed a prison compound in the northern city of Aleppo in a bid to free hundreds of political prisoners inside.
The forced retreat was the latest setback for fighters seeking to topple President Bashar Assad, whose forces have been gaining ground in the country's civil war.
In Washington, President Barack Obama and the Turkish prime minister projected a united front on Syria, despite sharp differences about how much the U.S. should intervene.
"There's no magic formula for dealing with an extraordinarily violent and difficult situation like Syria," Obama said at a joint news conference with Prime Minister Recep Tayyip Erdogan in which he pledged that the U.S. and Turkey would ramp up pressure to oust Assad from power.
Forces loyal to Assad have recently made advances in strategically important locations across the country, including in areas around the capital, Damascus, and in the country's south, near the border with Jordan.
The troops have been bolstered by the world's reluctance to take forceful action to intervene in the fighting, as well as the continued support from key allies, including Russia, Iran and the Lebanese militant group Hezbollah.
Assad has also benefited from the rapid rise of al-Qaida-linked extremists among the rebels, which has raised alarm in the West. Militant groups, including Jabhat al-Nusra, which is designated a terrorist group by the United States, have emerged as one of the most potent fighting forces in the uprising against Assad.
A video emerged Thursday showing a Nusra Front commander killing 11 regime soldiers execution-style for alleged crimes they committed against the Syrian people.
Rami Abdul-Rahman, director of the Syrian Observatory for Human Rights, whose group distributed the video, confirmed the killings took place late last year in eastern Deir el-Zour province and identified the Nusra commander as a Saudi known by the name Qusoura al-Jazrawi. He said the man was killed in March in battles with local gunmen in the tribal area.
The video shows the soldiers, blindfolded and kneeling in a row, as the masked commander shoots each one in the back of the head with what appears to be a pistol as other fighters shout "Allahu Akbar," or ""God is great."
"The Shariah court of Jabhat al-Nusra ... has sentenced to death these apostate soldiers that committed massacres against our brothers and families in Syria," the executioner says before firing at the men.
The video appeared authentic and consistent with AP reporting on the incident.
Thaer al-Deiri, an activist working with the Sham News Network in Deir el-Zour, said the execution-style killings occurred five months ago in a remote area in the western part of the province. It was not clear why the video only appeared Thursday, but al-Deiri said the Nusra Front apparently had released it.
Videos of executions and torture have become increasingly common in Syria's conflict, in which more than 70,000 people have been killed. Thursday's video follows a number of others purporting to show execution-style killings by rebels that have emerged in recent days in a war that largely plays out online due to the restrictions placed on journalists in Syria.
International rights groups have accused the rebels of routinely capturing and sometimes killing soldiers and suspected regime informers
Rebel abuses have increased in frequency and scale in recent months, according to a report by Amnesty International in March, which said the most common abuses on the rebel side are summary executions of those rebels suspected of being government soldiers.
The abuses by the Assad regime remain far more deadly, systematic and widespread, particularly attacks on civilians with imprecise battlefield weapons, including widely banned cluster bombs, rights group say.
On Thursday, the Obama administration added Jabhat al-Nusra leader Muhammad al-Jawlani to the U.S. terrorist backlist, along with four Syrian government ministers. Assets they have in the U.S. are blocked and Americans are prohibited from doing business with them.
Meanwhile, activists said the rebels were forced to retreat from the prison in Aleppo a day after they broke into the sprawling facility by setting off two simultaneous car bombs before dawn. By nightfall, the rebels had not dislodged regime forces or freed some 4,000 prisoners held inside.
The Observatory said Syrian warplanes bombarded areas around the prison causing casualties among rebels. State news agency SANA denied opposition fighters entered the prison compound, saying regime troops had repelled the attack.
But activists said fighting near the prison continued with rebels firing locally-made rockets at regime forces inside the facility late Thursday.
Also Thursday, four people were killed and 25 others wounded by mortar shells that struck residential areas in the town of Jaramana near Damascus, the state-run news agency said.
In Washington, Erdogan was looking for stepped-up action on Syria as he met with Obama just days after a twin car bombing killed 51 people on the Turkish side of the two countries' common border. Turkey blamed Syrian intelligence for the attacks.
The bombings Sunday in the border town of Reyhanli were the biggest incident of cross-border violence since the start of Syria's bloody civil war, raising fears of Turkey being pulled deeper into a conflict that threatens to destabilize the region.
But the Obama administration remains reluctant to take the kind of action Turkey would like to see, including establishing a no-fly zone in Syria.
The only way to resolve the crisis is for Assad to hand over power to a transitional government, Obama said.
"We both agree that Assad needs to go," the U.S. president said.
