BEIRUT -- After losing ground to Syrian forces and Islamic extremists for months, the Western-backed rebel movement announced Monday it was replacing its military chief with an experienced, moderate field commander from the south.

The move is part of a broader restructuring aimed at persuading the U.S. and its allies to provide more sophisticated weapons to confront President Bashar Assad's army after diplomatic efforts to end the war failed to take off.

U.S. Secretary of State John Kerry, meanwhile, accused Assad of stonewalling in peace talks and called on Russia to push its ally to negotiate with opposition leaders.

"Right now, Bashar Assad has not engaged in the discussions along the promised and required standard that both Russia spoke up for and the regime spoke up for," Kerry said during a news conference in Jakarta, Indonesia. He said it was clear the Syrian leader was "trying to win this on the battlefield instead of coming to the negotiating table in good faith."

The opposition reluctantly agreed to participate in two rounds of peace negotiations in Geneva, hoping it would convince the U.S. of the futility of a diplomatic track to end the country's three-year conflict. By revamping the opposition's moderate forces, it hopes to encourage its reluctant U.S. and European allies to send them anti-aircraft weapons to challenge Assad's monopoly on air power.

Brig. Gen. Abdul-Ilah al-Bashir replaces Gen. Salim Idris, a secular-leaning moderate who was criticized by many in the opposition for being ineffective and lost the confidence of the U.S. and its allies, particularly after Islamic extremists seized a weapons depot from moderate rebels. The move was announced Monday in a statement by the FSA's Supreme Military Council.

Al-Bashir, who previously headed the group's operations in the southern province of Quneitra on the border with the Israeli-occupied Golan Heights, is considered a moderate Islamist. He hails from the region's most powerful al-Nuaimi tribe, giving him influence among Syria's conservative rural areas, where tribal connections are important.

Rebels say he has vast knowledge of the areas south of Damascus where he served as an army commander until defecting to the opposition in 2012. His son Talal, also a rebel, was killed in battle with government forces in Quneitra last year.

In speeches, al-Bashir has said he supports a democratic Syria.

"The value of this man to the rebels is enormous. He was the commander of the Syrian army in the south, which included Daraa province and Golan area. These are the nearest points to Damascus," said Mustafa Alani, the director of the security department at the Geneva-based Gulf Research Center.

He said that after the failure of Geneva talks, Americans have realized that without escalating the military pressure on the Syrian regime, there will be no progress in the diplomatic process. "Now the diplomatic process is dead in the water," Alani said, adding that the U.S. was starting to relax the pressure on Gulf states who wished to supply the opposition with anti-aircraft weapons.

It's too early to tell whether al-Bashir will lean toward the West as his predecessor did, or move toward a rapprochement with jihadi groups in an attempt to halt infighting. Analysts say he will have to strike a delicate balance between the two to convince a reluctant West to arm the opposition.

Activists who know al-Bashir describe him as a devout, but not particularly conservative, Muslim. "He's a simple man, not an extremist," said a local activist, Jamal al-Golani.

Washington and its European allies have long tried to mould the Free Syrian Army into an effective partner inside Syria. But the loose umbrella group was always seen as weak, with Western and Arab allies dithering over whether to give them powerful weapons. The group eventually fell into disarray and in the past year has been overshadowed by more experienced Islamic groups and foreign fighters flush with cash.

More recently, the group has suffered a series of embarrassing setbacks, including the formation in November of the Islamic Front, a powerful alliance group for a mix of Islamic and nationalist brigades, many of whom broke away from the Free Syrian Army. In mid-December, Islamic extremists raided FSA weapons warehouses near the border with Turkey, leading to a temporary suspension of U.S. non-lethal aid to the rebels.

Amid declining international support for its fight to topple Assad, the group declared a war against an al-Qaida breakaway group, the Islamic State of Iraq and the Levant, one of the most powerful rebel forces in Syria. Hundreds of people on both sides have died in infighting since the beginning of the year.

By appointing al-Bashir, a decision made by consensus among the Free Syrian Army's 30-member Supreme Military Council late Sunday, the FSA hopes to show rival rebels that the group is re-energizing with a new, credible leadership.

The council appointed Col. Haitham Afiseh, an FSA commander in northern Syria, as al-Bashir's deputy.

"The new Supreme Military Council is now comprised of leadership that represent moderate Free Syrian Army forces on the ground which are actively fighting extremists and Assad's forces," said Monzer Akbik, a senior member of the Syrian National Coalition, the FSA's political wing.

The coalition's president, Ahmad al-Jarba, visited with rebel commanders in northern Syria at the weekend, including Jamal Maarouf, the powerful commander of the Syrian Revolutionaries Front, an FSA affiliate.

The Free Syrian Army has made other significant military reforms. In the days leading to January talks in Switzerland between opposition activists and Assad's representatives, the coalition formed a new northern front, and in February, a southern regional front, uniting chaotic groups.

"All of this is based, at least in some part, in trying to send a message to Western backers that moderates do still hold great potential strength in this conflict and they are capable of unifying their forces," said researcher Charles Lister, visiting fellow at the Brookings Doha Center.

Syria's conflict started in March 2011 as a largely peaceful uprising against Assad but eventually morphed into a civil war, with more than 140,000 people killed, according to activists.

Kerry had harsh words for Assad and his Russian backers Monday.

"Russia needs to be a part of the solution and not be contributing so many more weapons and so much more aid that they are in fact enabling Assad to double down, which is creating an enormous problem," he said.

In rebel-held parts of northern Syria where Islamic rebel groups prevail, al-Bashir's appointment was met with a shrug.

"Most of the factions on the ground are mostly of the Islamic Front who don't really care that Idris was fired, or that Bashir was appointed," said Akram al-Halabi, spokesman of the Tawhid Brigades, part of the Islamic Front.

"The people lost hope in the FSA a long time ago," he said.