Interactive Grid: Keeping track of the conflict in Syria through videos, images and tweets.

Nearly 93,000 people have been confirmed killed in the conflict in Syria, the United Nations said Thursday, as it warned that more bloodshed could be imminent in the northern city of Aleppo, where government troops have massed.

The conflict’s death toll is nearly two-thirds the number of fatalities recorded during neighboring Lebanon’s 15-year civil war, underscoring the intensity of the violence. And although 92,901 killings were documented in Syria in the 25-month period to April, the real figure is likely to be much higher, according to Navi Pillay, the U.N. high commissioner for human rights.

Lack of access for independent observers has presented problems in keeping track of deaths in the conflict. The U.N. numbers jibe with comments in late May by Secretary of State John F. Kerry, who said “upwards of 100,000” have been killed.

The increasingly sectarian violence on the ground, combined with a swing in President Bashar al-Assad’s favor, is forcing a reassessment of Syria policy among Western governments, with the White House holding crisis talks Wednesday to float options for better assisting the opposition.

With the resurgence of Assad’s forces, hopes have dimmed for U.S.- and Russian-backed peace talks, which are scheduled for July.

Timeline: Major events in Syria’s tumultuous uprising that began in March 2011.

“This extremely high rate of killings, month after month, reflects the drastically deteriorating pattern of the conflict over the past year,” Pillay said in a statement.

Speaking to Reuters TV, Pillay said she was “concerned” about a buildup of Syrian army troops near Aleppo after their victory in the strategic border town of Qusair this month. Pro-government media have been touting a new effort to seize rebel strongholds in an operation dubbed “Northern Storm.”

“All the reports I’m receiving are of augmentation of resources and forces on the part of the government,” she said.

The largest concentration of deaths has been in the rural areas outside Damascus, where 17,800 people have been killed, according to the U.N.-commissioned study.

The analysis used figures provided by eight sources, including the Syrian government. It is the first time a detailed study has been released since January. In mid-May, the United Nations said about 80,000 had been killed.

Violence continued around the capital Thursday as rebels attacked Damascus International Airport, disrupting flights, activists and officials said. The Britain-based Syrian Observatory for Human Rights said rebels had fired homemade rockets at the facility, and Syria’s transport minister told state television that a shell had injured a worker.