The United States is concerned about Syria's failure to live up to the "full spectrum of commitments" it made to the Arab League, State Department spokeswoman Victoria Nuland said on Tuesday.

She said that with monitors from the regional bloc on ground in Syria, the opposition had managed to organize demonstrations on the streets to press for changes by the government.

"More broadly, our concern is that the Syrian regime has not lived up to the full spectrum of commitments that it made to the Arab League when it accepted its proposal some nine weeks ago," the spokeswoman said at a regular press briefing.

She noted that violence has not stopped with the presence of monitors, with some 49 new deaths reported since the last day of 2011.

"The vast majority of these deaths have been at the hands of government troops, snipers, government armored personnel, et cetera," she remarked.

In addition, the Syrian government has not fully released political prisoners as promised, with the most high-level ones not among those being released, Nuland said.

The Arab League monitors entered Syria last week to conduct a field study of the situation in the Arab nation, which was plunged into turmoil in mid-March as anti-government protests broke out.

Nuland said that there is "sufficient concern" within the regional group about how the mission is going, and it had called a ministerial meeting for this Saturday to take stock.

"So we obviously will await that meeting. We support their efforts to ensure that this mission is credible, is effective if it's going to continue to go forward," she said. "We are in close touch with them."

She noted that U.S. Assistant Secretary of State Jeff Feltman was being sent to Cairo to consult with the Arab League on Syria and other issues ahead of the weekend meeting.

She warned against further militarization of Syria as the Free Syrian Army, an opposition armed force in the country, threatened on Tuesday to attack the government in a few days if the Arab League mission does not succeed in ending the violence.

"Our consistent view throughout this has been the view shared by the vast majority of Syrians in opposition, which is that further militarization of Syria, further violence in Syria is not the answer, is not the right move for the Syrian people," the spokeswoman said.

"That's exactly what the regime wants, to make Syria more violent and have an excuse to retaliate itself," she added.