BEIRUT » At least 141 people, half of them children, were killed when the Syrian military fired at least four missiles into the northern province of Aleppo last week, Human Rights Watch said today.

The international rights group said the strikes hit residential areas and called them an “escalation of unlawful attacks against Syria’s civilian population.” The statement from the New York-based group followed a visit to the area by a HRW researcher.

Aleppo, Syria’s largest city, has been the scene of some of the heaviest fighting of the civil war pitting President Bashar Assad’s regime against rebels bent on ousting him.

Rebels quickly seized several neighborhoods in an offensive on the city in July, but the government still controls some districts and the battle has developed into a bloody stalemate, with heavy street fighting that has ruined neighborhoods and forced thousands to flee.

A Human Rights Watch researcher who visited Aleppo last week to inspect the targeted sites, said up to 20 buildings were destroyed in each area hit by a missile. There were no signs of any military targets in the residential districts, located in rebel-held parts of Aleppo and its northern countryside, said Ole Solvang, the HRW’s researcher.

“Just when you think things can’t get any worse, the Syrian government finds ways to escalate its killing tactics,” Solvang said.

Human rights watch said 71 children were among the 141 people killed in the four missile strikes on three opposition-controlled neighborhoods in eastern Aleppo. It listed the names of the targeted neighborhoods as Jabal Badro, Tariq al-Bab and Ard al-Hamra. The fourth strike documented by the group was in Tel Rifat, north of Aleppo.

“The extent of the damage from a single strike, the lack of (military) aircraft in the area at the time, and reports of ballistic missiles being launched from a military base near Damascus overwhelmingly suggest that government forces struck these areas with ballistic missiles,” the report said.

Syrian anti-regime activists first reported the attacks last week, saying they involved ground-to-ground missiles, and killed dozens of people. The reports could not be independently confirmed because Syrian authorities severely restrict access to media.

Human Rights Watch said it compiled a list of those killed in the missile strikes from cemetery burial records, interviews with relatives and neighbors, and information from the Aleppo Media Center and the Violations Documentation Center, a network of local activists.

The rebels control large swaths of land in northeastern Syria. In recent weeks, Assad’s regime has lost control of several sites with key infrastructure in that part of the country, including a hydroelectric dam, a major oil field and two army bases along the road linking Aleppo with the airport to its east.

A key focus for the rebels in the Aleppo area is to capture the city’s international airport, which the opposition fighters have been attacking for weeks.

Opposition forces have also been hitting the heart of Damascus with occasional mortars shells or bombings, posing a stiff challenge to the regime in its seat of power.

U.S. and NATO officials have previously said that Syria has a significant ballistic missile capability and is believed to have a few hundred missiles with a range of some 700 kilometers (440 miles) that could hit targets deep inside Turkey, a NATO member and one of the harshest critics of the Assad regime.

NATO has in recent weeks deployed Patriot missile systems along Turkey’s border with Syria.

The missile attacks have outraged the leaders of the exiled opposition who have accused their Western backers of indifference to the suffering of the Syrian people.