Syrian President Bashar al-Assad faces the starkest test of his five-year presidency following an ultimatum from the United Nations that he cooperate with an international probe into the murder of a former Lebanese prime minister.
The choices the 40-year-old president makes in the next six weeks will decide the fate of his regime and the future of this country of 18 million citizens.
If President Assad fails to cooperate fully with the UN commission investigating the assassination of Rafik Hariri, Syria could face diplomatic isolation and crippling economic sanctions. But complying with the commission's demands could force Assad to gut his regime of its most powerful figures, including close relatives, potentially leaving it weakened and vulnerable.
UN resolution 1636 - passed unanimously on Monday by the 15-member Security Council - was a watered-down version of the original hard-hitting draft proposed by the United States, Britain, and France. Yet it still packs a punch, demanding that Syria hand over to UN investigators anyone suspected of "involvement in the planning, sponsoring, organizing, or perpetrating" of Mr. Hariri's assassination in February in a massive Beirut bomb blast that also claimed the lives of 22 others.
Additionally, if the UN commission investigating Hariri's murder determines that Syria is still not cooperating, the Security Council "could consider further action," an oblique reference to possible sanctions.
Syria has come under heightened international pressure since the UN commission reported on Oct. 20 that there is "converging evidence pointing at both Lebanese and Syrian involvement" in Hariri's death.
A confidential version of the UN report implicated key members of the Syrian regime, including President Assad's younger brother, Maher, who heads the powerful Republican Guard, and his brother-in-law, Assef Shawkat, the chief of military intelligence.
On Monday night, Detlev Mehlis, the German prosecutor heading the UN commission, returned to his headquarters outside Beirut. He is due to report back to the Security Council on Dec. 15, effectively giving Damascus a six-week deadline to satisfy UN demands.
In a sign of potential cooperation, Damascus announced over the weekend that it was setting up its own inquiry into the Hariri murder, appointing a three-member team of judicial figures who will question Syrian civilian and military officials and work closely with the UN commission and Lebanese authorities.
"The aim of this committee is to ensure cooperation with the Mehlis commission and ensure that there is conclusive and concrete evidence that would allow senior officials to be interviewed outside Syria," says Ayman Abdel-Nour, a reformist member of Syria's ruling Baath Party.
In his initial report, Mr. Mehlis accused Syria of having "impeded the investigation" through its "lack of substantive cooperation." In particular, the German prosecutor wants to interview Syrian witnesses and suspects away from the prying eyes of the regime, preferably at an overseas location.
But Syrian officials claim that the allegations contained in the report are biased and untrue, and analysts say the UN commission will have to provide clear evidence before the president hands over senior regime figures such as his brother, Maher, or brother-in-law, General Shawkat.
"The testimony of unnamed Syrian witnesses wishing to incriminate the regime is not considered valid evidence by the Syrians and certainly not enough reason for Syria to send its chief of intelligence for interrogation in Europe," says Sami Moubayed, a Syrian political analyst.
A key question that analysts ask now is whether Maher and Shawkat are indispensable components of the regime or whether they have become a dangerous liability through their alleged involvement in Hariri's murder. If the latter, can Assad sacrifice his brother and brother-in-law to ensure the survival of the regime?
"If he doesn't do it, then his country will face sanctions and become very vulnerable. If he does do it, then he will immediately get international support," says Patrick Seale, a veteran Middle East journalist and biographer of former President Hafez al-Assad, Bashar's father. "The crucial question is whether he has the support of the military chiefs."
Still, it is unclear whether President Assad has sufficient independent strength to remove two key members of his regime and survive the consequences.
"If you hand over these people, you would contribute to undermining the regime," says Marwan Kabalan, professor of politics at Damascus University. "The Syrian government might think that sanctions are a better alternative at the end of the day."
Damascus has embarked on a diplomatic campaign to shore up its waning international support, calling for an urgent meeting of the Arab League and dispatching Walid Muallem, the deputy foreign minister, on a tour of Arab nations.
President Assad is expected to make a rare address to the nation this week to reassure nervous Syrians worried about the consequences of sanctions on an ailing economy.
That unease is fostering a growing mood of anti-American nationalism among ordinary Syrians who view Resolution 1636 as a US-inspired punishment for Syria's opposition to the war in neighboring Iraq. On Tuesday, a few hundred people gathered outside the US embassy in Damascus to protest the resolution, the latest in a series of pro-regime demonstrations.
Analysts say that the Syrian regime can draw strength from that anti-American sentiment, possibly to ride out further international pressure.
"The regime is still very strong at a grass-root level in Syria. People still believe in President Assad, especially the youth," says Mr. Moubayed.
Still, many Syrians can't understand how their leaders have landed them in such an unenviable situation.
"If Hafez al-Assad was still president, he would have handled the situation we're in now in a different way. He had an understanding of international relations," says Mowafak al-Dibis, a watch-seller.