US aircraft carrier strike group arrives in Middle East

In his first public comments since the fall of Bashar Assad's government, Iranian Supreme Leader Ayatollah Ali Khamenei said Tehran and its regional allies will continue fighting against the U.S. and its allies in the Middle East despite setbacks for Iran in the region.

In a Wednesday morning speech in Tehran, Khamenei said the collapse of Bashar Assad's government -- of which Iran was a major patron -- was the product of a "joint" American and Israeli plan. "We have evidence -- this evidence leaves no room for doubt," he added.

Without naming Turkey, Khamenei said that one "neighboring state of Syria" also played an obvious role in the developments, but "the main conspirator, the main planner and the main command room are in America and the Zionist regime."

Iranian leaders have previously described the Syrian opposition forces that toppled Assad as "terrorists" or "rebels," but Khamenei on Wednesday did not use such words.

"Each of these fighters has a purpose," he said of the armed groups. "Their goals are different, some are seeking to seize territory from northern Syria or southern Syria."

The U.S., he added, "is seeking to strengthen its foothold in the region."

"Time will show that, God willing, none of them will achieve these goals," the ayatollah continued. "The occupied areas of Syria will be liberated by the zealous Syrian youth; do not doubt that this will happen."

Khamenei said that the Iranian-led "Resistance Front," meanwhile, will grow stronger despite its recent setbacks in Gaza, Lebanon and Syria.

"The more pressure you put on it, the stronger it becomes," he said of the grouping. "The more you fight them, the wider it becomes, and I tell you, with the power of god, the scope of resistance will encompass the entire region more than ever before," he said.

-ABC News' Somayeh Malekian

The United Nations Office for the Coordination of Humanitarian Affairs published a new report Wednesday warning that food prices in some parts of Syria have increased by 900% amid the collapse of former President Bashar Assad's regime.

"Food shortages were reported in Deir el-Zour, Damascus and Hama; bread prices Idlib and Aleppo rose by 900% from Nov. 27 to Dec. 9," the UNOCHA wrote, referring to the period between the start of the surprise rebel offensive in the northwest and the fall of Damascus.

"Around 100,000 individuals have been displaced to northeast Syria," the report continued. "Hospitals are overwhelmed with trauma and injury cases and there is significant psychological distress, especially among children," it added.

The "fluid displacements" of large numbers of people are particularly concerning given the many areas of continued fighting and minefields across the country, the UNOCHA said. Those include 52 minefields identified in the past 10 days, it said.

-ABC News' Somayeh Malekian

Syrian rebel forces said late Tuesday they had taken control of the eastern city of Deir el-Zour on the banks of the Euphrates River and close to U.S. military positions in the region.

The city was occupied by Kurdish-led Syrian Democratic Forces on Dec. 6 as former president Bashar Assad's forces withdrew. The SDF subsequenty faced protests from residents and local officials.

The Hayat Tahrir al-Sham Military Operations Department said in a post to Telegram that the city and its military airport were "completely liberated" as of the early hours of Wednesday.

Geolocated videos showed rebel fighters in the city center, joined by residents waving the Syrian revolutionary flag.

Rebel forces continued to advance into the countryside to the west and east of the city, Lt. Col. Hassan Abdul Ghani said in a statement posted to Telegram.

Deir el-Zour is the largest city in eastern Syria and the closest to U.S. troop concentrations along the Euphrates River running to the Iraqi border.

-ABC News' Helena Skinner

Iranian Supreme Leader Ayatollah Ali Khamenei alleged on Wednesday that the U.S. and Israel orchestrated the rapid collapse of the Syrian government led by former President Bashar Assad.

Damascus' defeat, Khamenei wrote on X, "was planned in the U.S.-Israeli control room."

"We have evidence for this" which leaves "no room for doubt," Khamenei said.

Iran and Russia were the key backers of Assad's government through more than a decade of civil war.

Tehran's support for the regime in Damascus enabled Iran's Islamic Revolutionary Guard Corps to establish a major presence inside Syria alongside a range of Iran-backed militias, including Lebanese Hezbollah.