Israel's military said it deployed additional tank and artillery forces on the Syrian front on Sunday as a precaution given intensified fighting over the border between the Syrian army and rebels.
"The forces deployed this morning as part of preparations and readiness, in light of developments on the Syrian Golan Heights," the military said in a tweet Sunday, adding that Israel was sticking to its longtime policy of nonintervention in Syria's civil war.
"The IDF will continue to maintain its noninvolvement in Syria while at the same time responding forcefully to any violation of Israel's sovereignty or endangerment of Israel's citizens," the IDF Spokesperson's Unit said in a statement.
In Syria, meanwhile, a string of rebel-held towns and villages accepted government rule on Saturday as insurgent lines collapsed in parts of southwest Syria under an intense bombardment that the United Nations says has forced 160,000 people to flee.
The southwest was an early hotbed of the uprising against Syrian President Bashar Assad and defeat there stands to leave rebels with just one remaining stronghold – the area around Idlib province bordering Turkey in the northwest.
Rebels met Russian negotiators on Saturday to seek peace terms for Daraa province, where most of their southwest territory is located but said these failed.
Moscow is Assad's strongest ally and its air power since 2015 has been crucial to his recapture of vast swathes of Syria.
Local groups in many towns seized by the army in recent days negotiated their own surrender deals independently of the main rebel operations, after heavy air raids.
Rebels said they had taken back several towns and villages lost to the army earlier in the day, but their overall loss of ground was still significant.
State television broadcast footage from inside the towns of Dael and al-Ghariya al-Gharbiya, where people were shown chanting pro-Assad slogans. A war monitor and a military media unit run by the government's ally Hezbollah said numerous other towns and villages had agreed to come back under Assad's rule.
Fierce battles were still ongoing around Daraa city, near the Jordanian border, where the army had repeatedly failed to capture a disused air base, rebels said. The northwestern chunk of Daraa province remains in opposition hands.
Air raids meanwhile intensified, said the monitor, the Syrian Observatory for Human Rights, as displaced people flocked to the border areas least likely to be hit.
U.N. High Commissioner for Human Rights Zeid Ra'ad al-Hussein warned, meanwhile, that many civilians in Syria were at risk of being trapped between government forces, rebels, and Islamic State which has a small foothold there – an outcome he said would be a "catastrophe."
"The real concern is that we are going to see a repetition of what we saw in eastern Ghouta – the bloodshed, the suffering, the civilians being held, being under a siege," U.N. human rights spokeswoman Liz Throssell said.
After the peace talks failed on Saturday, warplanes launched a new wave of strikes on the rebel-held towns of Bosra al-Sham, al-Nuaima and other areas, the Observatory reported, causing deaths, injuries and damage.
One strike killed at least 10 people including five children in the town of al-Sahwa, east of Daraa, it said, raising to 126 the number of civilians killed in the offensive since fighting escalated on June 19.
The army's offensive follows the capitulation of rebel enclaves near Homs and Damascus, including eastern Ghouta, which was recaptured after a scorched-earth assault that killed over a thousand civilians and laid waste to several towns.
Warfare in the southwest could risk a further escalation because of its proximity to Israel. The Israelis have already targeted Iran-backed militias fighting in support of Assad's army, which Israel has vowed to keep far from its borders.
The government's offensive so far has focused on Daraa province, which borders Jordan, but not Quneitra province abutting the Israeli Golan Heights.
The entire southwest is part of a "de-escalation zone" agreed upon last year by Russia, the United States and Jordan. Despite Washington's threats that it would respond to breaches of that arrangement, it has so far shown no sign of doing so.
Jordan, which has already taken in more than half a million displaced Syrians since the war began, and Israel have both declared that at this time they will not open their borders to refugees.
In an interview with Israeli radio station 102 FM, Israel's Energy Minister Yuval Steinitz said: "I think we must prevent the entry of refugees from Syria to Israel, in the past we have prevented such cases."
The Israel Defense Forces said an increased number of civilians had been spotted in refugee camps on the Syrian side of the Golan over the past few days, and that it had sent aid supplies at four locations to people fleeing hostilities.
Late on Saturday, the Jordanian government said its army had also started delivering humanitarian aid to thousands who had taken shelter across the frontier.
At the meetings with Russia, rebel negotiators sought a deal for all of Daraa province to come back under government sovereignty, but without the army or police entering the area, an insurgent spokesman said.
But the talks, in the town of Bosra al-Sham, whose Roman citadel is listed as a UNESCO world heritage site, collapsed as the insurgents rejected proposed terms for their surrender, a rebel spokesman said.
The Kremlin said Russian President Vladimir Putin and U.S. President Donald Trump will have a detailed discussion about Syria when they meet in July.
