US aircraft carrier strike group arrives in Middle East

State Department spokesperson Matthew Miller told journalists at a Monday briefing it is "obvious" that the U.S. wants to engage with Syrian rebel leaders including the head of the Hayat Tahrir al-Sham group, which is designated as a terrorist organization in the U.S.

Miller said the U.S. has "the ability to engage" with proscribed terror groups like HTS and is also speaking with the foreign backers of such groups and intermediaries within Syria.

HTS has roots in al-Qaeda and its leader -- Abu Mohammed al-Jolani -- fought with al-Qaeda against American occupation forces in Iraq. Jolani is still subject to a U.S. $10 million bounty.

Miller declined to say whether the U.S. will engage directly with Jolani, but said: "We want to have conversations with the key groups inside Syria, either directly or indirectly. It's obvious that HTS is one of them."

"I'm not ruling anything in or out either way," Miller added.

Jolani has sought to distance himself from his jihadist background in recent media and public appearances. The rebel leader said he is committed to a pluralist transition to a new government of national unity.

The U.K.-based Syrian Observatory for Human Rights watchdog said Tuesday that Israel has conducted around 310 airstrikes across Syria since the fall of former President Bashar Assad's regime on Sunday.

The group -- which documents war crimes and human rights abuses related to the Syrian Civil War and has generally been described as pro-opposition and anti-Assad -- said the targets included Syrian airports, aircraft, radars, air defense systems, scientific institutions and weapons and ammunition depots.

SOHR said Israeli strikes have been reported all across the country, from Deir Ez Zor in the east to the coastal province of Latakia in the west. Israeli strikes have reportedly hit targets in major cities including the capital Damascus, Aleppo, Hama, Homs and Daraa, SOHR said.

Israeli Foreign Minister Gideon Saar confirmed Monday that Israeli forces "attacked strategic weapons arrays, residual chemical weapons capabilities, missiles and long-range rockets" inside Syria to prevent them from falling into the hands of "extremist elements."

The Syrian Civil Defence, also known as the White Helmets, said it had concluded its search for detainees within Sednaya Prison on Monday after failing to uncover any "unopened or hidden areas" within the facility.

The prison previously held thousands of people detained by the former regime of ousted President Bashar al-Assad. Families of the missing and survivors believed that some detainees might have been unable to leave over the past two days, potentially due to being held in tightly sealed and secured areas, those close to the situation told the White Helmets, prompting the search.

"Specialized teams conducted a thorough search of all sections, facilities, basements, courtyards, and surrounding areas of the prison," the White Helmets said in a statement. "These operations were carried out with the assistance of individuals familiar with the prison and its layout. However, no evidence of undiscovered secret cells or basements was found."

The statement also called on international organizations and local authorities to support the efforts of the Syrian Civil Defence in uncovering the fate of the detainees and returning them to their loved ones.

"We share the profound disappointment of the families of the thousands who remain missing and whose fates remain unknown," the statement continued. "We stand in solidarity with the victims’ families, fully understanding their anguish and their longing for answers about their loved ones."

-ABC News' William Gretsky

Secretary of State Antony Blinken said senior officials from his department are "fanning out through the region as we speak" to work with their counterparts on how the U.S. can "help support the Syrian people as they decide their own path for the future."

"We have a strong interest in preventing the reemergence of ISIS, given the death and destruction that it has wrought for so long,” he said during remarks at an unrelated event on Monday.

Blinken noted that ISIS would seek to exploit the moment, and that U.S. strikes on ISIS sites over the weekend demonstrate that the U.S. is "determined not to let that happen."

"We have a clear interest in doing what we can to avoid the fragmentation of Syria, mass migrations from Syria and, of course, the export of terrorism and extremism," he said. "The region and the world have a responsibility to support the Syrian people as they begin to rebuild their country and charge a new direction."

Blinken also said that with every party they engage with, he and other U.S. officials will continue to seek information on American freelance journalist and Marine Corps veteran Austin Tice, who went missing while covering the civil war in August 2012, "so that we can find him and bring him home to his family and loved ones."

-ABC News' Shannon K. Kingston