BEIRUT, Lebanon — The Syrian government fired at least four ballistic missiles last week that hit civilian neighborhoods in Aleppo, Syria’s largest city, killing more than 141 people, including 71 children, according to a Human Rights Watch report released on Tuesday.
Syrian antigovernment activists had reported the missile strikes last week, corroborated by video of the aftermath posted on the Internet, but the Human Rights Watch report contained new details about the number of missile strikes and the scope of destruction, with a death toll that was far higher than previously thought.
“The extent of the damage from a single strike, the lack of 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.
The assessment came as both sides’ international backers called with increasing urgency for a political solution but remained unable to get the antagonists to talk. That impasse has been the main focus of the first foreign trip by John Kerry, the new American secretary of state, who met with his Russian counterpart, Foreign Minister Sergey V. Lavrov, on Tuesday to try to push the Syrian combatants into talks.
Fighting intensified in Aleppo, including around the 12th-century Umayyad Mosque, one of the architectural centerpieces of Aleppo’s Old City, and around a long-contested police academy, according to rebels and the government.
The ballistic missile strikes felled entire buildings in destruction that stands out even after months of fighting, according to Human Rights Watch. Its researchers visited all four sites, in residential areas, and found no evidence of military targets nearby, making the attacks a violation of international law, the organization said.
A resident of Ard al-Hamra, one of the neighborhoods hit, said he had just left his brother’s house after evening tea on Friday when “the sky was lit up by a tremendous flash and all air was sucked away.”
He ran back to find that “my brother’s house was gone,” he told Human Rights Watch. “We managed to find my five young nieces and nephews, aged between 3 and 17 years old. They were all dead under the rubble. We still have not found my brother. When will somebody stop this madness?”
As the death toll from the Syrian conflict exceeds 70,000, according to United Nations estimates, and the destruction of major cities continues unabated, fears are mounting that the conflict will spread throughout the region.
Jeffrey D. Feltman, the United Nations’ top political official, told the Security Council during a Middle East briefing, “The destructive military spiral churns more forcefully each day and threatens to pull its neighbors, most notably and worrisomely Lebanon, into its vortex.”
Lebanon, torn apart by political disagreements over Syria and longstanding sectarian divides exacerbated by the increasingly sectarian killing in Syria, last week became the country hosting the largest number of Syrian refugees, even though it is Syria’s smallest and most politically vulnerable neighbor.
“Even tentative steps to dialogue are struggling to take root,” Mr. Feltman said, referring to offers of negotiations issued — with caveats and conditions — by both the Syrian opposition and government in recent days. “Regrettably, the warring parties remain locked in military logic which is bound to bring more death and destruction.”
Before a meeting in Rome on Thursday of the opposition’s international backers, the main opposition group remains under pressure to further unify and organize itself — in part to make sure there is someone for the government to meet with should talks become possible.
The opposition group, the National Coalition of Syrian Revolutionary and Opposition Forces, has said that on Saturday it will select a prime minister to run an interim government to be established in rebel-held areas of northern Syria. But the group has set and missed such deadlines in the past, and members say there is no consensus yet on who should fill the post.
Even if a prime minister is appointed and empowered to negotiate with the Syrian government, it is unclear if talks will take place. The government of President Bashar al-Assad, backed by Russia, has long insisted that Mr. Assad be part of the process, while the opposition coalition, backed by the United States, declares that he cannot be.
Seeking to resolve that impasse, Mr. Kerry had his first meeting as secretary of state with Mr. Lavrov of Russia on Tuesday in Berlin.
The meeting covered the range of American-Russian issues, from economic relations to adoption of Russian orphans. But more than half of the session was devoted to the situation in Syria.
Hillary Rodham Clinton, Mr. Kerry’s predecessor as secretary of state, believed she had worked out an agreement with the Russians in Geneva in June that would have established the framework for negotiations on a political transition to a post-Assad government. But the Russians interpreted the agreement differently, saying that the understanding that Mr. Assad should leave power could not be a precondition for the talks.
Mr. Kerry, who has said he has new ideas on how to advance diplomacy on Syria, has been looking for a way to secure Russian backing for a transition.
“It was a really serious and hard-working session,” said Victoria Nuland, the State Department’s spokeswoman. Much of the discussion, she said, “focused on Syria and how we can work together to implement the Geneva agreement.”
Mr. Lavrov told Russian news agencies after the meeting that Russia would try to establish the conditions for initiating “a dialogue between the government and the opposition.”
