The United States on Monday accused 13 Syrian commanders and prison officials of responsibility for attacks on cities, residential areas and civilian infrastructure as well as acts of torture.

U.S. Ambassador Samantha Power read out the names of Maj. Gen. Adib Salameh, Brig. Gen. Adnan Aboud Hilweh, Maj. Gen. Jawdat Salbi Mawas, Col. Suhail Hassan, and Maj. General Tahir Hamid Khalil at a Security Council meeting, saying the international community is watching "and one day they will be held accountable."

The detailed allegations appeared to be aimed at laying the groundwork for future war crimes prosecutions and marked an 11th hour attempt by the Obama administration to hold the Syrian government accountable for alleged atrocities.

Power accused President Bashar Assad's regime and close ally Russia of continuing their "starve, get bombed, or surrender" strategy in rebel-held eastern Aleppo and stressed that this was not an isolated case.

"Across Syria, Russia and the Assad regime are waging a campaign that includes sieges, the blocking of humanitarian aid, the indiscriminate bombardment of civilian areas, and the use of barrel bombs," she said.The United States also knows where torture allegedly takes place in Syria, she said, citing four military intelligence branches, the Air Force Intelligence Investigation Branch in Mezzeh military airport, and the Tishreen and Harasta military hospitals.

Power named eight commanding officers and prison officials who work at these facilities saying the United States "will continue fighting to hold them accountable for their hateful crimes."

She identified them as Maj. Gen. Jamil Hassan, Brig. Gen. Abdul Salam Fajr Mahmoud, Brig. Gen. Ibrahim Ma'la, Col. Qusai Mihoub, Brig. Gen. Salah Hamad, Brig. Gen. Sha'afiq Masa, Maj. Gen. Rafiq Shihadeh, and Hafiz Makhlouf.

The U.S. Mission said Makhlouf, Hassan and Mihoub are already subject to U.S. sanctions.

"I know right now, today, with wind at their backs, these individuals feel impunity," Power said, but she reminded them that others who felt that way including Bosnian Serb leader Slobodan Milosevic and Liberian president Charles Taylor were eventually arrested and brought before the International Criminal Court.

Power said the United States recognizes that opposition groups and Islamic State extremists have also committed abuses, but she didn't identify any individuals.

Russia's deputy ambassador Vladimir Safronkov demanded to know "where are the names of the terrorists?"

"You need to be impartial," he told Power. "There's a presumption of innocence. ... This is something that can only be decided by legal proceedings."

When Syria's Ambassador Bashar Ja'afari was called on to address the council, Power walked out of the chamber along with the British and French ambassadors, Matthew Rycroft and Francois Delattre.

Safronkov called the walkout "unacceptable behavior."

Ja'afari defended the bombing campaign saying Syria was "fighting a terrorist statelet."

But U.N. humanitarian chief Stephen O'Brien strongly criticized Assad's government for invoking national sovereignty "to bomb its own people."

He said the number of Syrians living in areas besieged mainly by government forces has more than doubled in the past year to nearly one million people.

"It is a deliberate tactic of cruelty to compound a people's suffering for political, military and in some cases economic gain, to destroy and defeat a civilian population who cannot fight back," O'Brien said.

In eastern Aleppo, he said, humanitarian conditions have gone "from terrible to terrifying and now barely survivable."