Syrian President Bashar al-Assad is set to regain control of his country's frontier with Israel in a major victory over rebels who have agreed to surrender in negotiations with Russia, sources on both sides say.

The resumption of Syrian control over areas bordering the Israeli-occupied Golan Heights, one of the last remaining rebel strongholds in the country, appears to be part of a larger Russian plan to reinstitute Syrian control in the border region while clearing the area of pro-Iranian militias, as sought repeatedly by Israel and the United States in talks with Moscow this year.

Backed by Russian air power, Assad's forces have swept through southwestern Syria in the last month in one of the swiftest campaigns of the seven-year civil war, forcing surrender on massively outgunned rebels.

The campaign has already restored Assad's control over a critical portion of the border region with Jordan. The latest negotiated surrender marks another milestone in Assad's Russian-backed effort to reassert rule over a country fractured by a war that has killed more than 400,000 people.

Syrian state media reported that a deal for Quneitra Province in the southwest had been reached and said 10 buses entered a village in Quneitra late on July 19 for the evacuation of insurgents "who refused to settle with the state" to rebel territory in the north.

A copy of the surrender agreement sent to Reuters by a rebel source said insurgents had negotiated the deal with Russia.

Echoing surrender terms imposed on rebels elsewhere in the country, opposition fighters agreed to give up their heavy and medium-sized weapons. Those wishing to stay in the area agreed to "settle" their status with the state, meaning accept the return of Assad's rule.

Rebels who rejected the surrender terms were given safe passage and transport to the opposition-held province of Idlib in the northwest.

The terms of the surrender deal were also reported by the Syrian Observatory for Human Rights, a London-based war monitor, and a military news outlet run by Lebanon's Hizballah, an Iranian-backed militia that has fought in support of Assad.

Reports said an affiliate of the Islamic State extremist group continued to hold a sliver of the Golan frontier and it is not party to the agreement.

What Comes Next?

Once the southwestern campaign is finished, officials said Assad's focus is likely to turn to the two remaining areas outside his grasp.

These are the rebel-held northwest, where the presence of Turkish forces will complicate any military campaign, and large areas of the northeast and east that are held by Kurdish-led militias, which are supported by 2,000 U.S. troops on the ground there.

As Damascus and its allies continue to make substantial gains on the battlefield, chances appear to be dwindlng for a UN-brokered peace deal, which Assad's adversaries say is needed to stabilize the country and encourage millions of refugees to return.

In addition to killing hundreds of thousands of people, the UN estimates that the Syrian civil war has displaced 11 million people and forced 6 million abroad as refugees.

The campaign near the Golan frontier has been particularly sensitive because of Israeli concerns. Israel has signaled it has no problem with Assad regaining control of the area as long as Iranian military advisers and Tehran-backed militias do not accompany his troops.

Israeli Prime Minister Benjamin Netanyahu held talks with Russian President Vladimir Putin about the matter last week in Moscow, one day before a top adviser to Iranian Supreme Leader Ayatollah Ali Khamenei met with Putin.

Russia's ambassador to Syria, Aleksandr Kinshchak, told Russian news services in Moscow on July 19 that the south of Syria near Israel had now been cleared of Iranian-allied groups.

"This issue has already been settled. I have repeatedly heard from different sources that there are no pro-Iranian, Shi'ite units in the south of Syria," he was quoted as saying by state-run news agency TASS.

The United States may have also been involved in the deal. U.S. President Donald Trump said at a news conference after his summit with Putin on July 16 in Helsinki that the two leaders had agreed to work together to help ensure Israel's security.

Israel this year has repeatedly warned Iran not to beef up its military presence in Syria, and has staged several deadly air strikes against what it said were Iranian and Hizballah positions and facilities in Syria.

The latest surrender deal by rebels puts the Syrian government face-to-face with Israel along most of its frontier for the first time since 2011, when an uprising against Assad's rule ushered in the civil war.

Syria and Israel fought two wars over their shared border, in 1967 and 1973, leading to Israel's seizure of the Golan Heights in what was part of Syria's Quneitra Province. The Israeli occupation has never been recognized internationally.

In accepting the return of the Syrian Army to the border region, Israel has said it would demand strict adherence to a 1974 disengagement deal that created a buffer zone patrolled by a UN Disengagement and Observer Force.

The rebel surrender deal seen by Reuters included a provision saying Russian military police would accompany the Syrian Army to the frontier area in a bid to ensure Damascus adheres to the 1974 cease-fire agreement.

With reporting by Reuters, TASS, AP, and AFP