The United Nations last month announced the long-awaited formation of the committee to include 150 members, split evenly between Syria's government, the opposition and Syrian civil society.

While the mandate of the body has not been precisely defined -- it remains unclear if it will aim to write a new constitution or adjust the existing one -- some experts were surprised that President Bashar al-Assad's government agreed to participate at all.

Ahead of the committee's first meeting, set for Geneva next week, Washington's special envoy for Syrian James Jeffrey told reporters that the Assad regime is actively trying to thwart the process.

"The amount of effort that the Syrian government has put into not having this occur is for us a good indicator that the Syrian government fears that this assembly, and the political momentum that it will represent, is inimical to its desire to achieve a total military victory," he said.

"We are very aware of steps they are trying to take to make this thing as ineffective as possible," he added.

Constitutional review is a central part of the UN-led effort to end the war in Syria, which has killed more than 370,000 people and displaced millions since erupting in 2011 with the repression of anti-government protests.

The UN peace effort, governed by Security Council resolution 2254, also calls for UN-supervised elections in Syria.