Assassination in Damascus

For 17 months, President Bashar alAssad of Syria has waged bloody war against his people from his redoubt in Damascus, convinced that he could weather the storm. A bombing on Wednesday that killed at least three of his most senior aides — including the defense minister and Mr. Assad’s powerful brother-in-law — shows that the war can reach deeply into the capital.

There were conflicting news reports about the cause of the explosion. State television reported that it was carried out by a suicide bomber, while the main armed opposition group said explosive devices were detonated remotely.

There is no condoning such tactics, and it is impossible to know whether the assassination is any kind of a turning point. The armed opposition is obviously making gains, but there is still no sign that Mr. Assad is planning to leave power. He has proved to be even more brutal than his father and could crack down even harder on the opposition. Reports that his government is moving its stockpile of chemical weapons and might be preparing to use them are especially alarming.

What is clear is that any chance that the United States and other Western powers could still facilitate a dip- lomatic solution is rapidly fading, largely because of months of Russian intransigence. Everyone’s concern should be the thousands of Syrian civilians who have died at Mr. Assad’s hand and the thousands more still hounded by his security forces with helicopters and tanks.

But the United Nations Security Council has postponed until Thursday a vote on whether to extend the mission of 300 monitors sent to Syria to oversee a peace plan — including a cease-fire and a political transition — to which Mr. Assad agreed three months ago but has repeatedly reneged on. The work of the unarmed observers was suspended because of the violence.

The United States and other Western nations have said they would extend the mission only if the Security Council adopts a resolution with some teeth, one that would threaten Mr. Assad with enforceable sanctions if he continues to thwart the peace plan. The United States and the European Union long ago imposed their own sanctions on Syria — the American penalties were toughened on Wednesday — and they are having an effect. But United Nations sanctions would have a much greater impact and are urgently needed.