The top American diplomat blamed a resurgence of the Islamic State extremist group in areas outside of the transitional government's control, as well as Iran.

He told a US Senate hearing that the government, "given the challenges they're facing, are maybe weeks -- not many months -- away from potential collapse and a full-scale civil war of epic proportions, basically the country splitting up."

Rubio spoke after a series of bloody attacks on the Alawite and Druze minorities in Syria, where Islamist-led fighters in December toppled then-president Bashar al-Assad, capping a brutal civil war that began in 2011.

US President Donald Trump last week on a visit to Saudi Arabia announced a lifting of Assad-era sanctions and met with the guerrilla leader who is now Syria's transitional president, Ahmed al-Sharaa.

Sharaa, clad in a suit and complimented by Trump as a "young, attractive guy," was until recently on a US wanted list over jihadist connections. 

Rubio quipped: "The transitional authority figures, they didn't pass their background check with the FBI."

But he added: "If we engage them, it may work out, it may not work out. If we did not engage them, it was guaranteed to not work out."

Rubio, who also met with Syria's foreign minister in Turkey on Thursday, said Iran was looking to work with remnants of the fallen ally Assad, a largely secular leader who hailed from the Alawite sect.

Rubio acknowledged concerns about Syria's direction in Israel, which has kept pounding military sites in the neighboring country.

But Rubio, who has spoken twice in recent days to Israeli Prime Minister Benjamin Netanyahu, said a more stable Syria that did not serve as a "launchpad for attacks" would be an "extraordinary achievement for Israel's security."

European Union countries, which had already suspended economic sanctions on Syria, gave the green light on Tuesday to lift all restrictions.

"We want to help the Syrian people rebuild a new, inclusive and peaceful Syria," top EU diplomat Kaja Kallas wrote on X after the bloc's foreign ministers met in Brussels.

EU diplomats said that move would unfreeze central bank assets and help reintegrate Syrian banks to the global system, although sanctions would remain on individuals over stirring ethnic tensions.

Syria's foreign ministry hailed the EU decision, saying it marked "the beginning of a new chapter in Syrian-European relations built on shared prosperity and mutual respect."

Syrian Foreign Minister Asaad al-Shaibani, welcoming his Jordanian counterpart to Damascus, said at a joint news conference that "the doors are open" for investment in Syria with the lifting of sanctions.

The United States had previously insisted on key steps from Syria's transitional authorities, including protection of minorities.

Trump's move on Syria was encouraged by Turkey -- the main patron of the Islamist fighters who had battled Assad, an ally of Iran and Russia -- and Sunni regional power Saudi Arabia.

"The nations in the region want to get aid in, want to start helping them, and they can't because they're afraid of our sanctions," Rubio said.

Rubio has said Trump plans to waive the Caesar Act, which imposed sanctions for investment on Syria in an effort to ensure accountability regarding abuses under Assad.

But such waivers would be temporary, and Syria remains classified by the US as a state sponsor of terrorism, a major impediment to business dealings.

Rubio, asked if the administration sought to delist Syria from its terrorism blacklist, replied: "Yes, if they meet the standard."