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Syria’s rebels launched a bold attack in Damascus Wednesday, unleashing a bomb during a high-level security meeting that killed three top officials in the regime, including President Bashar Assad’s brother-in-law.

State-run TV said the blast came during a Cabinet meeting of senior officials in Damascus, which has seen four straight days of bloodshed.

The killings could signal a change in the civil war, a turning point that has seen the violence escalate and grow more chaotic.

U.S. Defense Secretary Leon Panetta said the bombing showed that the bloodshed in Syria was "rapidly spinning out of control," and it was time for the international community to bring "maximum pressure" on Assad to step down and permit a stable transfer of power.

Panetta’s remarks came as the Obama administration put financial sanctions on a huge swath of top members in Assad's government, targeting the prime minister and 28 other Cabinet ministers and senior officials.

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    The U.N. Security Council delayed a vote on a new Syria resolution until Thursday in a last-minute effort to get key Western nations and Russia to reach agreement on measures to end the dramatically escalating violence.

    International envoy Kofi Annan urged the deeply divided council to delay Wednesday afternoon's scheduled vote after the bombing.

    U.N. Secretary-General Ban Ki-moon, who was visiting China, also urged the Security Council to "take collective action, with a sense of unity."

    State-run TV reporter that the three senior Syrian government officials killed are Gen. Dawoud Rajha, who took over as defense minister last August; Gen. Assef Shawkat, the deputy defense minister and Assad’s brother-in-law who was a trusted aide; and Gen. Hassan Turkmani, a former defense minister who was serving as an assistant to the country's vice president.

    Meanwhile, Russia, a longtime ally of Syria, is accusing the West of inciting the Syrian opposition following the deadly rebel assault.

    In Israel, Defense Minister Ehud Barak summoned his top security and intelligence advisers to discuss the deteriorating security situation in Syria.

    Israel has stayed out of the fighting, but is fearful that Syrian weapons could reach anti-Israel militants. On Tuesday, Israel's military intelligence chief said Islamist militants may exploit the power vacuum to attack Israel. Syria and Israel are bitter enemies, but their border has been mostly quiet since 1974.

    The Assad family has ruled Syria for four decades, creating an ironclad and impenetrable regime. Wednesday's attack was an unheard-of strike on the inner circle.

    Syria's rebel commander, Riad al-Asaad, said his forces carried out the attack.

    Although state-run TV said it was a suicide blast, al-Asaad said his rebel forces planted a bomb in the room and detonated it. All those involved in carrying out the attack are safe, he said.

    "God willing, this is the beginning of the end of the regime," al-Asaad told The Associated Press in a telephone interview from his base in neighboring Turkey.

    "Hopefully Bashar will be next," he added.

    It was not immediately clear where Assad was; he gave no immediate statements on the attacks, although in the hours after the assassination, Syria's state-run TV said a decree from Assad named Gen. Fahd Jassem al-Freij as the new defense minister. Al-Freij used to be the army chief of staff.

    Republican Guard troops surrounded the nearby al-Shami Hospital, where some officials were taken for treatment, witnesses said.

    The attack came two days before the beginning of the Muslim holy month of Ramadan, when observant Muslims abstain from eating, drinking and sex from dawn to dusk. Last year, anti-government protests sharply increased during Ramadan.

    The last major attacks on regime figures and government buildings date back to the early 1980s, when members of the Syrian Muslim Brotherhood were waging a guerrilla war to topple the regime of Assad's father and predecessor, President Hafez Assad.

    The Associated Press contributed to this report.