BEIRUT, Lebanon -- Syrian insurgents seized control of a northern military airfield on Tuesday and captured usable warplanes for the first time in the nearly two-year-old conflict, according to rebels and activist groups. The development, if confirmed, would represent the second strategic setback for President Bashar al-Assad's government this week.
The reported seizure of Al Jarrah airfield in Aleppo Province, which was corroborated by rebel video clips uploaded on the Internet, came a day after insurgent fighters announced that they had taken control of Syria's largest hydroelectric dam, which supplies power to areas held by Mr. Assad's security forces and by the insurgent Free Syrian Army and affiliated rebel groups. Whoever controls that dam, situated on the Euphrates River in northeast Raqqa Province, theoretically has the ability to deny electric power to significant areas held by the other side.
It was far from clear whether the insurgency's claimed military gains signaled a bigger turn in the conflict, but some political analysts said they believed that the claims were credible and noteworthy. "Combined with capturing the dam, it's another sign that Assad's power is degrading but not yet finished," Andrew J. Tabler, a senior fellow in the Program on Arab Politics at the Washington Institute for Near East Policy, said in an e-mail.
The developments coincided with a sharply higher estimate of total casualties in the conflict -- nearly 70,000 -- from the top human rights official at the United Nations, Navi Pillay, in a report to the Security Council, which has been deadlocked on how to deal with Syria. Less than two months ago, Ms. Pillay said more than 60,000 had died in Syria since the uprising against Mr. Assad began in March 2011.
She exhorted the Security Council to take action, saying, "We will be judged against the tragedy that has unfolded before our eyes."
The Syrian Observatory for Human Rights, an anti-Assad group based in Britain with a network of contacts inside Syria, said the Syrian Air Force had responded to the Jarrah seizure by bombarding it, presumably to destroy or incapacitate the planes there. The observatory said in a Facebook post that the rebels had "taken control of tens of military jets," mostly Soviet-era MIG-17s and Sukhoi L-39 jet fighters. "This is considered the first instance of rebels acquiring fighter jets," the group said.
More than 40 Syrian soldiers were captured by the rebels, with an unspecified number of others killed and wounded, the group said, and the rebels confiscated ammunition and machine guns.
The triumphal video clips posted on YouTube by the Jarrah attackers included one showing rebels inside the facility, with a background voice yelling: "Allahu akbar, our spoils are planes! You pigs of Bashar!"
Another video shows a queue of parked jet fighters out in the open near a runway, most apparently intact but at least one crumpled.
By late Tuesday it was unclear if any planes of the Jarrah-based fleet had suffered damage, either in the two-day siege by the insurgents to capture the airfield, or in the Syrian Air Force's response. Syria's official SANA news agency, in its daily report on insurgent fighting, said the army had inflicted "heavy losses upon terrorists in several provinces," but said nothing about the Jarrah airfield.
Earlier instances of rebel seizures of military airfields have been met with ferocious reprisal bombings by Mr. Assad's military, which would rather destroy the planes and other weaponry than lose them to the rebles. Syrian forces also have fired Scud missiles at suspected insurgent positions, according to opposition activists and Western intelligence officials. But the Scuds, not known for their precision, have hit civilians as well. The Local Coordination Committees, a network of anti-Assad groups, reported on Tuesday that three Scuds had landed in Barouda, a small village in Raqqa Province, destroying at least one house.
The addition of aircraft to the rebel arsenal is a potentially significant military development if any of the pilots who have defected to the insurgency are capable of flying them. Up until now, President Assad has been able to contain or repel insurgent gains in many parts of the country because of his side's overwhelming air power.
But even if rebel pilots can start fighting the Syrian Air Force in the sky, they remain heavily outgunned, a reality that some fighters acknowledged on Tuesday in Skype interviews following news of the Jarrah airfield capture. One suggested that the planes could be used in kamikaze raids on Mr. Assad's loyalists.
"It is very hard to use these warplanes because the regime has radars and long-distance rockets, unless it is a suicidal attack," said the fighter, who identified himself only by his first name, Saado, for security reasons.
Another fighter reached via Skype from a group affiliated with the Nusra Front, a brigade of jihadists known for their fearless fighting skills but blacklisted by the Obama administration because of suspected links to Al Qaeda in Iraq, said there were "many pilots who defected and they are ready to use these jets." The fighter, who spoke on the condition of anonymity, said rebels were also in control of an unspecified number of captured helicopters, and "most of them are still working." It was impossible to corroborate those claims.
Hwaida Saad reported from Beirut, and Rick Gladstone from New York. Hania Mourtada and Anne Barnard contributed reporting from Beirut.
This article originally appeared in The New York Times.