BEIRUT, Lebanon -- Syrian antigovernment activists said on Tuesday that an army rocket had leveled several buildings in a rebel-held neighborhood of Aleppo, killing at least 19 people and possibly leaving dozens more buried under rubble. The attack appeared to have caused one of the worst civilian tolls in the embattled city since its university was struck in a multiple bombing a month ago.
Activists also reported that up to seven mortar rounds had been fired by fighters of the Free Syrian Army toward President Bashar al-Assad's Tishreen Palace in Damascus. There were no immediate reports of casualties, and it was not known if Mr. Assad had been there at the time. The palace, surrounded by a park, is in an upscale area that has largely been insulated from the insurgency and is situated less than a mile from the main presidential palace, on a plateau overlooking the city.
An activist contacted in Damascus, Suzan Ahmad, said that the palace had been targeted in the mortar assault, and that at least one round had made a direct hit. Syria's official news agency, SANA, said two mortar rounds had landed near two hospitals and the palace's southern wall, resulting in "material damage only." It did not provide further details. SANA said the rounds had been fired by terrorists, the government's name for armed insurgents.
The Syrian Observatory for Human Rights, an anti-Assad group based in Britain that has a network of sources in Syria, described the Aleppo rocket as a "surface-to-surface missile" that slammed into the Jabal Badro neighborhood late on Monday, and it said at least six children and three women were among the victims. A witness in Aleppo was quoted by Reuters as saying that the attack had felled three buildings, and that survivors were digging up bodies.
Syria's state-run news media did not immediately report on the rocket attack, and it was impossible to independently corroborate the details provided by the anti-Assad activists. But the attack appeared to be one of the deadliest in the city since more than 80 people were killed and hundreds were wounded on Jan. 15 in a multiple bombing of Aleppo University as students were taking exams. Although rebels and the government accused each other of responsibility for the attack, video footage of the immediate aftermath suggested that it had involved a missile or missiles fired by the Syrian military.
The United Nations has estimated that 70,000 people have died in the Syrian conflict, which began as a peaceful uprising against Mr. Assad in March 2011. The alliance of rebel groups fighting to oust Mr. Assad has claimed a series of strategic advances in recent weeks, but Mr. Assad contends that his side is winning.
In Geneva, where the United Nations has been coordinating a response to the humanitarian crisis caused by the conflict, senior aid officials said on Tuesday that Syria's government had allowed more international organizations to participate but had been impeding or preventing their efforts to deliver emergency supplies.
"The Syrian government must stop obstructing the delivery of humanitarian assistance," Nancy Lindborg, the assistant administrator of the United States Agency for International Development, said at a meeting of aid officials, called the Syria Humanitarian Forum.
United Nations agencies reported this week that the access across lines of conflict negotiated with government and opposition forces had enabled them to deliver relief supplies to 65,000 people since the end of January, but they estimated the number of people in desperate need of assistance at four million, four times the level in mid-2012.
"We are not reaching enough of those who need our help," Valerie Amos, the United Nations humanitarian relief coordinator, told reporters in Geneva after the meeting. "We are watching a humanitarian tragedy unfold before our eyes."
Ms. Amos also told reporters that the United Nations was pressing donor nations to make good on their pledges of $1.5 billion announced at a conference in Kuwait last month. The United Nations has received only 20 percent of the $519 million it is seeking for Syria relief during the first half of 2013.
The United States announced in Geneva that it would provide an additional $19 million in aid, mostly for medical assistance in Syria and food aid for refugees in neighboring countries, bringing total American assistance to more than $384 million, including $216 million for relief inside Syria and $168 million for refugees.
Anne Barnard reported from Beirut, and Rick Gladstone from New York. Hwaida Saad and Hania Mourtada contributed reporting from Beirut, and Nick Cumming-Bruce from Geneva.
This article originally appeared in The New York Times.