President Barack Obama's chief of staff says it's only a matter of time before the government of Syrian President Bashar Assad collapses.
Jacob Lew says the U.S. and its allies have brought "serious financial pressure" on Syria and that Assad's government is "feeling it."
While the violence continues as rebels try to topple Assad, Lew says the transition "from tyranny to democracy is very hard." Lew says the Syrian people "have to handle this in a way that works in Syria."
Lew tells "Fox News Sunday" that "the brutality of the Assad regime is unacceptable and has to end." He says the U.S. is pursuing "all avenues that we can" and that "there is no question that this regime will come to an end. The only question is when."
Meantime, Tunisia says it will host the inaugural meeting of the "Friends of Syria" group to explore ways to further isolate President Bashar Assad, support his foes and end violence.
Tunisian Foreign Minister Rafik Abdessalem told a meeting of Arab League foreign ministers in Cairo that his North African nation was ready to host the Feb. 24 meeting.
U.S. calls for a meeting of the Friends of Syria group followed the veto by Russia and China last weekend of a Western and Arab attempt at the U.N. to pressure Assad to step down.
The Tunisia meeting will bring together the United States, its European allies and Arab states working to end Syria's turmoil.
Al-Qaida's chief has called on Muslims from other countries to support rebels in Syria seeking to overthrow President Bashar Assad, saying they cannot depend on the West for help.
Ayman al-Zawahri, in a videotaped statement released late Saturday, asked Muslims in Iraq, Jordan, Lebanon and Turkey to join the uprising against Assad's "pernicious, cancerous regime." All four states border Syria.
A senior Iraqi security official also told the Associated Press on Saturday that intelligence over the last four months has revealed a flow of al-Qaida-linked fighters from the northern Iraqi city of Mosul into Syria.
The comments by both the Iraqi official and al-Zawahri came a day after two suicide car bombers struck security compounds in Aleppo, a Syrian city that had been relatively peaceful throughout the country's 11-month-uprising. Though there was no claim of responsibility, suicide bombings are a hallmark of al-Qaida.
"There is no treatment for (the Assad regime) other than removal," al-Zawahri says in the eight-minute video posted on jihadist websites, according to U.S.-based SITE Intel Group, which monitors militant messages.
"Don't depend on the West and Turkey, which had deals, mutual understanding and sharing with this regime for decades and only began to abandon it after they saw it faltering," he said. "Instead, depend on Allah alone and then on your sacrifices, resistance, and steadfastness."
He urged Syrians to oppose help from the Arab League and "its corrupt agent governments." The League has put forth a plan to try to end violence in Syria but it suspended an observers mission to the country after the regime flouted its agreement to the terms of the plan.
Hours later, a Sunni sheik in Iraq's northern Kurdish region said a group of clerics in the area is calling for a Muslim jihad, or holy war, against Assad's regime.
"Jihad is the duty of every Muslim against the Assad regime," said Sheik Abdul-Rahman Abdul-Karim Barzanji, describing the edict issued by the Union of the Scholars of Islam in Kurdistan. "Any support from any Muslim or country is forbidden."
"Jihad" is literally translated as "holy war" but Islam dictates also interpret it as supporting fighters with money or other support — and not necessary fighting.
Egyptian-born al-Zawahri took over al-Qaida after Osama bin Laden was killed last May by a U.S. special forces raid on his hideout in Pakistan.
The Iraqi official said at least two Syrian suicide bombers who trained in Mosul have crossed the border to join the fight in Syria.
Fighters armed with guns and explosives also have headed from Iraq to Syria, said the official, who spoke on condition of anonymity because he was not authorized to publicly discuss intelligence.
A U.S. official in Washington, who also spoke on condition of anonymity, said it would not be surprising if Iraqi al-Qaida fighters are aiding Syrian rebels, but would not discuss or confirm specific intelligence. However, the official noted that al-Qaida in Iraq long has had an operational network in Syria.
Al-Zawahri in the past clashed with al-Qaida in Iraq. Both he and bin Laden urged followers to focus attacks against U.S. and Israeli interests, and sharply condemned the network's Iraqi wing for targeting Shiite Muslims during the years that Iraq teetered on the brink of civil war.
Al-Qaida fighters in Iraq generally have confined attacks to their home country.