Overnight, the Islamist-led government's troops withdrew from the predominantly Druze city of Sweida, where scores of people have been killed in days of conflict.
One local journalist said he had counted more than 60 bodies in the streets of Sweida on Thursday morning.
Ryan Marouf of Suwayda24 told Reuters he had found a family of 12 people killed in one house, including women and an elderly man.
"People are looking for bodies," he said in a voice recording. Violence in Syria escalated sharply on Wednesday as Israel launched air strikes in Damascus, while also hitting government forces in the south, demanding they withdraw and saying Israel aimed to protect Syrian Druze - part of a small but influential minority that also has followers in Lebanon and Israel.
Israel, which bombed Syria frequently under the rule of ousted President Bashar al-Assad, has struck the country repeatedly this year, describing its new leaders as barely disguised jihadists and saying it will not allow them to deploy forces in areas of southern Syria near its border.
Addressing Syrians on Thursday, interim President Sharaa accused Israel of seeking to "dismantle the unity of our people", saying it had "consistently targeted our stability and created discord among us since the fall of the former regime".
Sharaa, who was commander of an al Qaeda faction before cutting ties with the group in 2016, said protecting Druze citizens and their rights was "our priority" and rejected any attempt to drag them into the hands of an "external party".
He also vowed to hold to account those who committed violations against "our Druze people".
The Syrian Network for Human Rights said it had documented 193 dead in four days of fighting, among them medical personnel, women and children.
The Network's head Fadel Abdulghany told Reuters the figure included cases of field executions by both sides, Syrians killed by Israeli strikes and others killed in clashes but that it would take time to break down the figures for each category.
US Secretary of State Marco Rubio said late on Wednesday the United States had engaged all the parties involved and that steps had been agreed that would end "this troubling and horrifying situation".
Sharaa credited US Arab and Turkish mediation for saving "the region from an uncertain fate".
A Turkish security source said Ankara played a crucial role in securing the ceasefire.
The violence has underlined the challenges that Sharaa faces in stabilising Syria and exerting centralised rule over the country, despite his warming ties with the United States and his administration's evolving security contacts with Israel.
Sharaa faces challenges to stitch Syria back together in the face of deep misgivings from groups that fear Islamist rule. In March, mass killings of members of the Alawite minority exacerbated the mistrust. The Druze follow a religion that is an offshoot of Islam.
Israel's air strikes on Wednesday blew up part of Syria's defence ministry and hit near the presidential palace as it vowed to destroy government forces attacking Druze in southern Syria.
"We will not allow southern Syria to become a terror stronghold," said Eyal Zamir, Israel's military chief of staff.
The United Nations Security Council will meet on Thursday to address the conflict.
Scores of Israeli Druze broke through the border fence on Wednesday, linking up with Druze on the Syrian side.
Israeli Prime Minister Benjamin Netanyahu urged Israeli Druze citizens not to cross the border, and the military said it was working to safely return civilians who had crossed.
