BEIRUT, Lebanon — Syrian forces continued to press an intense counteroffensive against rebels in the Damascus suburbs on Tuesday, as the government blamed rebels for a mortar attack that hit a school, and the United Nations warned that the increasingly dangerous situation in the country was making it hard to provide enough food to displaced Syrians.

The state news agency, SANA, reported that 10 people at the school, 9 students and a teacher, were killed by a mortar shell fired by “terrorists,” its term for its opponents, in Bteeha, a small town north of Damascus on the road to the central city of Homs. Antigovernment activist groups confirmed the attack, but put the death toll at nine. The road to Homs and on to the commercial hub of Aleppo has been strongly contested in recent fighting.

The Local Coordination Committees, a network of rebel groups, reported the mortar attack without comment, implying that it was carried out by the government. But an activist reached in Damascus said it was unclear who had fired the shell. Recent bombs and mortar attacks by rebels that have killed civilians have angered both supporters and opponents of the government, as even some who support the rebels express concern that the violence has spiraled out of control.

An activist in the Damascus suburbs who gave only her first name, Leena, said that activists were surprised there was an attack in Bteeha, which is usually very calm, and that information had been hard to come by because very few activist reporters were in Bteeha. She said that many residents were refugees who fled the Golan Heights in 1967 when Israel occupied the territory, and that displaced people, mostly from the Sunni Muslim sect that makes up the bulk of the Syrian uprising, have recently moved there.