Middle East live updates: IDF says Israelis entered Lebanon in 'serious incident'

Mouaz Moustafa, the head of the U.S.-based Syrian advocacy organization, the Syrian Emergency Task Force, told ABC News there are believed to be well over 100,000 bodies in a "massive" burial site discovered 25 miles north of Damascus.

Moustafa told ABC News from the Syrian capital that the site in al-Qutayfah consists of "massive graves" where "lines or trenches were 6 to 7 meters deep, 3 to 4 meters wide and 50 to 150 meters long."

"In my conversation with the gravediggers, they told me that four tractor trailer trucks each carrying over 150 bodies came twice a week from 2012 until 2018," Moustafa said.

"The bulldozer excavator driver described how intelligence officers forced workers to use the bulldozer to flatten and compress the bodies to make them fit and easier to bury before digging the next line or trench," he added.

The mass grave contained men, women, children and the elderly "tortured to death" by former President Bashar Assad's regime, Moustafa said.

The overthrown president was in power from 2000 to his ousting on Dec. 8. In his first statement since fleeing Syria, Assad on Monday blamed a "terrorist onslaught" for his defeat. His toppling marked the end of a 14-year conflict between Damascus and a collection of rebel groups.

Opposition groups and rescue workers are still uncovering evidence of the regime's human rights abuses. SETF believes it has identified three other mass graves so far, as well as two "smaller ones," Moustafa said.

-ABC News' Guy Davies

Israel "will have security control over Gaza with full freedom of action" after the fighting in the devastated Palestinian territory ends, Israeli Defense Minister Israel Katz said in a post to X on Tuesday.

Katz added that Israeli access to the strip will be comparable to its access to the occupied West Bank, which is nominally controlled by the Palestinian Authority but in coordination with Israel.

"We will not allow any terrorist organization against Israeli communities and Israeli citizens from Gaza," Katz wrote. "We will not allow a return to the reality of before Oct. 7."

Prime Minister Benjamin Netanyahu's government has faced domestic and international criticism for its failure to present a clear vision for post-war Gaza beyond the destruction of Hamas as a ruling force.

President Joe Biden is among the world leaders that have warned Israel against any post-war occupation of Gaza or permanent displacement of Palestinians.

The State Department's lack of boots on the ground in Syria isn't interfering in its efforts to track down missing American journalist Austin Tice, spokesperson Matthew Miller contended on Monday.

The department has had "more than one communication" with rebel group HTS "over the past week," he told reporters. It was also in touch with other groups, like the White Helmets, that were helping with the search, he said.

"We feel that right now we are able to get good information," he said.

Tice, an American freelance journalist and Marine Corps veteran, was kidnapped while reporting in Syria more than a decade ago.

In a recent letter to Israeli Prime Minister Benjamin Netanyahu obtained by ABC News, Tice's family "urgently" asked the Israelis to pause their strikes in a neighborhood in Damascus where they believe he may be held prisoner and to deploy assets to the area to help search for him.

"I'm going to be looking for help anywhere I can, and what I've learned in 12 years and four months is go to the top first," Tice's mother, Debra Tice, told reporters on Monday when asked about the outreach.

"I think it would be polite to say the least, that perhaps they’re not bombing as people are trying to clear the prison. That would be my first suggestion," she added.

ABC News has reached out to the prime minister's office for comment.

-ABC News' Shannon K. Kingston and Will Gretsky

Israeli officials are expressing optimism about the prospects of a ceasefire deal in Gaza.

"We are closer to a deal than in any other point since the previous deal, the matter is top priority," Israeli Defense Minister Israel Katz said while addressing the Knesset on Monday, according to the spokesperson of the foreign affairs and security committee.

The remarks come after Mossad chief David Barnea traveled to Doha, Qatar, last week for ceasefire negotiations.