Thousands of Syrians celebrate in central Damascus during first Friday prayers since Assad's fall

Blinken arrived in Iraq on a previously unannounced stop after talks in Jordan and Turkey, which backs some of the Syrian insurgent factions. So far, U.S. officials have not talked of direct meetings with Syria's new rulers.

The main insurgent force, Hayat Tahrir al-Sham, has worked to establish security and start a political transition after seizing Damascus early Sunday. The group has tried to reassure a public both stunned by Assad's fall and concerned about extremist jihadis among the rebels. Insurgent leaders say the group has broken with its extremist past, though HTS is still labeled a terrorist group by the United States and European countries.

HTS's leader, Ahmad al-Sharaa, formerly known as Abu Mohammed al-Golani, appeared in a video message Friday congratulating "the great Syrian people for the victory of the blessed revolution."

"I invite them to head to the squares to show their happiness without shooting bullets and scaring people," he said. "And then after, we will work to build this country, and as I said in the beginning, we will be victorious by the help of God."

Syrians celebrate in the historic heart of Damascus

Huge crowds, including some insurgents, packed Damascus' historic Umayyad Mosque in the capital's old city, many waving the rebel opposition flag — with its three red stars — which has swiftly replaced the Assad-era flag with with its two green stars.

According to Arab television stations, the Friday sermon was delivered by Mohammed al-Bashir, the interim prime minister installed by HTS this week.

The scene resonated on multiple levels. The mosque, one of the world's oldest dating back some 1,200 years, is a beloved symbol of Syria, and sermons there like all mosque sermons across Syria had been tightly controlled under Assad's rule.

Also, in the early days of the anti-government uprising in 2011, protesters would leave Friday prayers to march in rallies against Assad before he launched a brutal crackdown that turned the uprising into a long and bloody civil war.

"I didn't step foot in Umayyad Mosque since 2011," because of the tight security controls around it, said one worshipper, Ibrahim al-Araby. "Since 11 or 12 years, I haven't been this happy."

Another worshipper, Khair Taha, said there was "fear and trepidation for what's to come. But there is also a lot of hope that now we have a say and we can try to build."

Blocks away in Damascus' biggest roundabout, named Umayyad Square, thousands gathered, including many families with small children — a sign of how, so far at least, the country's transformation has not seen violent instability.

"Unified Syria to build Syria," the crowd chanted. Some shouted slurs against Assad and his late father, calling them pigs, an insult that would have previously led to offenders being hauled off to one of the feared detention centers of Assad's security forces.

One man in the crowd, 51-year-old Khaled Abu Chahine — originally from the southern province of Daraa, where the 2011 uprising first erupted — said he hoped for "freedom and coexistence between all Syrians, Alawites, Sunnis, Shiites and Druze."

The interim prime minister, al-Bashir, had been the head of a de facto administration created by HTS in Idlib, the opposition's enclave in northwest Syria. The rebels were bottled up in Idlib for years before fighters broke out in a shock offensive and marched across Syria in 10 days.

Similar scenes of joy unfolded in other major cities, including in Aleppo, Homs, Hama, Latakia and Raqqa.

US and its allies try to shape a rapidly changing Syria

Al-Sharaa, HTS' leader, has promised to bring a pluralistic government to Syria, seeking to dispel fears among many Syrians — especially its many minority communities — that the insurgents will impose a hard-line, extremist rule.

Another key factor will be winning international recognition for a new government in a country where multiple foreign powers have their hands in the mix.

The Sunni Arab insurgents who overthrew Assad did so with vital help from Turkey, a longtime foe of the U.S.-backed Kurds. Turkey controls a strip of Syrian territory along the shared border and backs an insurgent faction uneasily allied to HTS — and is deeply opposed to any gains by Syria's Kurds.

In other developments, Turkish Foreign Minister Hakan Fidan said Turkey's Embassy in Damascus would reopen Saturday for the first time since 2012, when it closed due to the Syrian civil war.

The U.S. has troops in eastern Syria to combat remnants of the Islamic State group and supports Kurdish-led fighters who rule most of the east. Since Assad's fall, Israel has bombed sites all over Syria, saying it is trying to prevent weapons from falling into extremist hands, and has seized a swath of southern Syria along the border with the Israeli-occupied Golan Heights, calling it a buffer zone.

After talks with Fidan, Blinken said there was "broad agreement" between Turkey and the U.S. on what they would like to see in Syria.

That starts with an "interim government in Syria, one that is inclusive and non-sectarian and one that protects the rights of minorities and women" and does not "pose any kind of threat to any of Syria's neighbors," Blinken said.

Fidan said the priority was "establishing stability in Syria as soon as possible, preventing terrorism from gaining ground, and ensuring that IS and the PKK aren't dominant" — referring to the Islamic State group and the Kurdistan Workers Party.

Ankara considers the PKK within Turkey's borders a terrorist group, as it does the Kurdish-backed forces in Syria backed by the U.S.

A U.S. official said that in Ankara, President Recep Tayyip Erdogan and Fidan both told Blinken that Kurdish attacks on Turkish positions would have to be responded to. The official spoke to reporters on condition of anonymity to discuss private diplomatic talks.

The U.S. has been trying to limit such incidents in recent days and had helped organize an agreement to prevent confrontations around the northern Syrian town of Manbij, which was taken by Turkey-backed opposition fighters from the U.S.-backed Kurdish forces earlier this week.

In Baghdad, Blinken met with Iraqi Prime Minister Mohammed al-Sudani, saying both countries wanted to ensure the Islamic State group — also known by its Arabic acronym Daesh — doesn't exploit Syria's transition to re-emerge.

"Having put Daesh back in its box, we can't let it out, and we're determined to make sure that that doesn't happen," Blinken said.

The U.S. official who briefed reporters said that Blinken had impressed upon al-Sudani the importance of Iraq exercising its full sovereignty over its territory and airspace to stop Iran from transporting weapons and equipment to Syria, either for Assad supporters or onward to the militant Hezbollah group in Lebanon.