At least 16 people, most of them students, have been killed in an air attack that hit a high school in the rebel-held Syrian city of Raqqa, opposition activists say.
Graphic amateur video said to be filmed on Sunday in Raqqa showed several bloodied bodies strewn across a dirt yard, some torn in half.
Opposition activists based in Raqqa, a northeastern city of about 250,000 people, said there were more than 30 people wounded in addition to the fatalities.
Al Jazeera could not independently verify the reports because of reporting restrictions in Syria.
Raqqa has been under the control of fighters battling to overthrow President Bashar al-Assad since March, but the city remains subject to regular aerial bombardment by government forces.
Farther south, government forces shelled near the Ramtha border crossing in Deraa near Jordan on Sunday, a day after rebels — including fighters affiliated with al-Qaeda — seized control of the post, which had served as the customs office on the border with Jordan.
Al Jazeera's Nasser Shadid, reporting from Deraa, said that while the border crossing was now under the control of the rebels, the surrounding area was still controlled by regime troops.
"Clashes are continuing between the two sides," he said.
The Jordanian state news agency reported on Sunday that a shell from fighting in Syria landed in Jordan on Thursday night, prompting the Foreign Ministry to send a written protest to the Syrian Embassy in Amman.
In August last year, four rockets fired from Syria crashed in northern Jordan near the border, wounding a young girl.
Jordan has taken in more than 500,000 Syrian refugees.
Meanwhile, in the suburbs of Damascus, opposition groups upheld a cease-fire from 11 a.m. to 12 p.m. in towns under their control, Al Jazeera's Mahmoud Zaibak reported on Sunday, after an agreement with U.N. monitors, who returned to Syria last week to investigate sites of alleged chemical attacks.
He said the lull in fighting was implemented in the town of Zamalka and the Damascus districts of Qaboun and Jobar.
Also on Sunday, at least four vehicles belonging to the U.N. inspectors were seen returning to the Four Seasons Hotel in Damascus after departing that morning. Their destination was not known.
The experts are to investigate seven sites of alleged chemical attacks in the country, four more than previously known.
The U.N. said the team expects to finalize its activities in the country by Monday.
The inspectors, who visited Syria last month, determined that the nerve agent sarin was used in an attack of the Damascus suburb of Ghouta on Aug. 21, but it did not assess who was behind it.
The U.N. Security Council adopted a resolution on Friday that demands the elimination of Syria's chemical arsenal.
On Sunday, Assad told Italian television station RaiNews24 that his country would respect the resolution, saying, "We joined the international agreement against the acquisition and use of chemical weapons even before this resolution was passed."
The measure is the first U.N. resolution on Syria's conflict, which has lasted 30 months and, the U.N. says, has left more than 100,000 dead.
Al Jazeera and wire services