Speculation in the Middle East is intensifying about the apparent assassination of a powerful figure within the Syrian president’s inner circle, and Syria observers say the incident could prove a “source of embarrassment” to the once all-powerful Assad regime.

Syrian officials made no comment yesterday about the death of Brigadier General Mohammad Suleiman, whose title as a Baath Party leader betrayed none of his considerable power. The 49-year-old Suleiman, who grew up with President al-Assad and his brothers, is said to have held such sensitive military positions as point man on Lebanon and Hezbollah and chief of a nascent Syrian nuclear facility that was bombed last September, reportedly by Israel.

A dissident group led by an exiled former Syrian vice president, Abdul-Halim Khaddam, said that on Friday night, a sniper shot Suleiman from a yacht near the port city of Tartous.

The president’s brother Maher al-Assad and brother-in-law Assef Shawkat attended his funeral Sunday. Both men have been accused in U.N. reports of involvement in the killing of a former Lebanese prime minister, Rafik Hariri.

Israel would not risk a war with Syria by killing Suleiman amid ongoing indirect peace talks with Damascus, an anonymous Israeli told the British television network Sky News. “An Iranian spy might be killed in Lebanon, a Hezbollah guy in Syria, but not a Syrian in Syria with a sniper,” the source said.

One Syrian opposition group, the Reform Party of Syria, said it had nothing to do with the killing but that other opponents of the regime could be responsible. Hezbollah officials were uncharacteristically quiet, while Mr. Assad was on a state visit to Iran yesterday, where neither he nor his hosts mentioned Suleiman. The killing went unreported in Syria’s state-controlled press.

Among the suspects in Suleiman’s assassination are Israel, which could have been trying to avert a future military attack led by Suleiman, or seeking revenge for his role in supplying arms to Hezbollah during the 2006 war; Hezbollah, as revenge for the assassination in Damascus of its operations commander, Imad Mughniyeh, a close associate of Suleiman; Iran, for the same reason, or because of possible negligence in defending the bombed nuclear facility; elements within the Assad regime, as part of a power struggle, or out of fear that Suleiman knew too much about the Hariri killing, and dissident Syrian groups.

“Nothing would surprise me,” the director of Middle Eastern studies at Tel Aviv University’s Moshe Dayan Center, Eyal Zisser, said.

In contrast to the regime of Saddam Hussein in Iraq, the Syrian leadership, which runs the country like a “Mafia family,” has not killed its insiders, Mr. Zisser said. “Suleiman was certainly one of a handful of people who helped Assad control Syria,” he said. “This is a source of embarrassment for the regime, especially coming after the nuclear plant bombing and the Mughniyeh assassination.”

“I cannot underestimate his importance,” the president of the Washington-based Reform Party, Farid Ghadry, said of Suleiman. “We are not involved,” he added, though he did not rule out other dissident groups as being behind the killing.