(CNN) -- Armed, masked men raise their weapons and shoot dead three men sitting on a curb in a Syrian city. The images are captured on video, purportedly showing Islamist rebels carrying out a public execution of soldiers.
The incident occurred in Raqqa city, in the north. Videos produced by locals sympathetic to the Islamists have appeared on the Web, and an opposition group, the Syrian Observatory for Human Rights issued a report on the incident Tuesday.
"Rebel fighters from the Islamic State of Iraq and Bilad al-Sham (Syria) have summarily executed three men in the middle of a square in Raqqa city," the Observatory said. "The jihadis stated that the detainees were officers from the Syrian army."
The videos show armed masked men standing in a street, with one of them reading from a paper. A crowd of onlookers can be seen in the background. Gunmen shoot dead three men who are sitting on a curb and the militants raise their weapons in celebration.
There was no immediate comment on the incident from rebel leaders and the government.
This is the latest report of an atrocity in a war rife with abuse, killing and widespread population displacement.
Since the unrest began in March 2011, Syrians have described a range of human rights abuses by security forces and backers of President Bashar al-Assad's regime.
There have been claims of atrocities by rebels forces as well.
The Raqqa incident comes on the heels of a horrific video showing a man said to be a Syrian rebel carving into the body of a government soldier, cutting out his heart and liver, and putting the heart in his mouth, taking a bite.
Other violence persisted Wednesday. Clashes broke out between rebel fighters and regime troops at the Aleppo central prison, the Syrian Observatory for Human Rights said. The Israeli military said several Syrian rockets landed in the Mount Hermon area of the Israeli-occupied Golan Heights, on the border with Syria.
At least 50 people were killed Wednesday across the country, the opposition Local Coordination Committees of Syria said. Of those, 18 were in Aleppo and four were in Raqqa.
Meanwhile, the Internet is back up again in Syria after being down for more than eight hours Wednesday, according to the Renesys Corp., an Internet monitoring company. A week ago, a widespread Internet outage in Syria lasted more than 19 hours before access was restored.
In Sweden Wednesday, U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov discussed the revival of a peace initiative based on last year's Geneva conference.
That conference, brokered by Russia and the United States, outlined how a transitional government could be formed in Syria.
"I think it's fair to say that both of us are confident about the direction that we're moving in and very, very hopeful that within in a short period of time, the pieces will have come together fully so that the world, hopefully, will have an opportunity to be given an alternative to the violence and destruction that is taking place in Syria at this moment," Kerry said.
Lavrov cited the Russian-American proposal to convene a conference to start implementing the Geneva communique last June.
"It's self-explanatory, and what we need now is to mobilize support for this initiative on the basis of what was, I believe, in Geneva and what was proposed by Washington and Moscow: to mobilize support, first of all, by all the Syrian groups, the regime and all opposition groups; and second by those outside actors who have influence on either one or the other Syrian group," Lavrov said.