The new U.S. chief envoy for Syria on Monday pledged continued American backing for political opponents of Syrian President Bashar al-Assad as the country’s conflict moves into a fourth year.

“Assad will go to any length to maintain power,” Daniel Rubinstein said in a YouTube message in Arabic. “This year, let us remember and honor all those who have suffered as a result of the Assad regime’s response” to the opposition.

Rubinstein takes over the envoy job this week as U.S.-backed peace talks have stalled and rebels are losing ground on the battlefield. A key rebel-held town fell to Syrian government forces over the weekend.

Rubinstein is a longtime diplomat and Middle East expert. He succeeds Robert Ford, the last U.S. ambassador to Syria, a position the Obama administration now calls the American representative to the Syrian people.

Since the Obama administration closed the U.S. Embassy in Damascus in 2012, Ford has spent much of his time shuttling between Washington and Turkey, where the main Syrian opposition group is based. He was instrumental in bringing the opposition to peace talks in Geneva this year despite wide reservations among some leaders that talking to Assad’s representatives would weaken their influence with rebels on the front lines.

The talks went nowhere and are in limbo. They represented the only means the Obama administration has advanced to end the uprising, which passed its third anniversary over the weekend.

Rubinstein is expected to follow Ford’s model of frequent contact with opposition groups, despite the current impasse. Announcing Rubinstein’s appointment Monday, Secretary of State John F. Kerry said Rubinstein would travel to the region soon but gave no details.

“This week is indeed a somber occasion and a sober reminder to all of us of the work still ahead — and the United States will stand with you,” Rubinstein said in his message, also posted on the Web site for the U.S. Embassy in Damascus.