Israeli Defense Minister Ehud Barak on Wednesday praised the United States and other countries for ousting Syrian diplomats but said it was not sufficient, declaring that the massacre of 100 people in Houla “compel the world to take action — not just talk, but action.”

“I don’t think that Assad lost an hour of sleep last night because of those people leaving,” Mr. Barak said of the Syrian president, Bashar al-Assad. “More concrete action is required,” he added. “These are crimes against humanity and it’s impossible that the international community is going to stand aside.”

Mr. Barak’s comments, made during a wide-ranging speech at the annual conference here of Israel National Security Studies — a prominent research organization close to the Israeli military and security establishment — were the strongest to date by an Israeli leader regarding the Syrian regime. In his own speech to the conference Tuesday night, Prime Minister Benjamin Netanyahu also referred critically to Syria, describing the regime as “slaughtering its own citizens so cruelly.”

At the same time, in an interview on Army Radio Wednesday morning, Deputy Prime Minister Shaul Mofaz said that Israel should consider providing humanitarian relief along its border with Syria in the Golan Heights. “The West must intervene, either directly or indirectly,” Mr. Mofaz said. “We, too, have to think about ways we can help, and it is worth at least preparing for an eventuality where we could also open up an aid corridor.”

Neither Mr. Netanyahu nor Mr. Barak prescribed a specific plan against Syria, but both noted its connections to Iran and Hezbollah, the heavily armed Shiite Muslim group, a relationship that Mr. Barak described as “a radical axis” and “an unholy alliance.”

It was Iran that occupied the bulk of Mr. Barak’s nearly hourlong speech in a tent here on the campus of Tel Aviv University. He compared the current moment to the one Israel faced before the 1967 war, calling the Iranian nuclear threat “a sword on the neck” of the Jewish state.

“You don’t wait until they acquire the capability and they build it and they deploy it — then it’s too late, you cannot act,” Mr. Barak said. “The Iranians are patient. They say to themselves, ‘We waited 4,000 years until we have a nuclear power, we can wait another four weeks or four months or four quarters.

“You cannot sleep quietly when the Iranians are going to the point that after that Israel will not be able to do anything,” he added. “Israel doesn’t have an option, and I repeat does not have an option, to ignore this challenge.”

Almost as an afterthought, Mr. Barak closed with comments about the conflict with the Palestinians, saying for the first time that if negotiations regarding a final-status solution remain stalemated, Israel should consider unilateral action — like its pullout from the Gaza Strip seven years ago — or an interim agreement.

“Inaction is not a possibility,” Mr. Barak said, referring to the Israeli concern that Palestinians could soon outnumber Jews in the land between the Mediterranean Sea and the Jordan River that both peoples claim rights to. “Israel cannot afford stagnation. “We should have marked borders between the states and we should have a majority Jewish population in Israel and we can have a Palestinian state besides us that is a realization of their dreams,” he added. “It will be a difficult decision to make, but time is running out.”

Prime Minister Netanyahu on Tuesday night gave the Palestinian issue primacy in his own address to the conference, saying that his new unity government, with a huge majority of 94 of the 120 members of Parliament, presents “a unique opportunity.”

“Do not miss the opportunity to extend your hand in peace,” he said, theoretically addressing Mahmoud Abbas, the president of the Palestinian Authority. “Chances are not always repeated in history, in political history, but it exists now and negotiations for peace need two sides. One side is there.”