Shimon Peres, Israel’s president and elder statesman, spoke out Thursday against the prospect of a lone Israeli military strike on Iran’s nuclear facilities, a message that contradicts the hawkish, go-it-alone line emanating from the offices of Israel’s prime minister and defense minister.

The president’s comments came amid a wave of speculation in Israel and abroad that Prime Minister Benjamin Netanyahu and his defense minister, Ehud Barak, might be weighing the option of a unilateral strike even before the American presidential elections in November, while Israel’s limited military capabilities might still have an impact.

“Now, it is clear to us that we cannot do it alone,” Mr. Peres told Israel’s Channel 2 television in an interview marking his 89th birthday. “We can delay,” he said, referring to the partial damage that Israel’s military could do to the Iranian nuclear program, adding: “It is clear to us that we have to proceed together with America. There are questions about coordination and timing, but as serious as the danger is, this time at least we are not alone.”

Mr. Peres was careful to avoid personal criticism of the political leadership, and the prime minister’s office did not issue any official response. But the Israeli news media widely quoted a sharp retort attributed to “people close to the prime minister,” accusing Mr. Peres of forgetting his place and overstepping his role as president, and castigating him for serious mistakes they said he had made in the security realm in the past.

The interview was broadcast hours after Mr. Barak told the Israeli Parliament that the risks and complications of dealing with Iran today would be less dangerous and less costly than dealing later with a nuclear Iran.

It remains unclear to what extent Mr. Netanyahu and Mr. Barak are serious about attacking, or whether the idea is more to use the credible threat of an attack to press Washington and rest of world into imposing tougher sanctions on Iran or even into declaring a commitment to American-led military action at some later date.

It was also unclear whether Mr. Peres was speaking out of intimate knowledge of the leadership’s thinking, or merely expressing his own hope.

The Israeli president’s role is largely ceremonial and plays no part in government decision-making, although Mr. Netanyahu has conferred closely with Mr. Peres on certain issues in the past and Mr. Peres maintains close ties with foreign leaders. Mr. Peres last met with President Obama in Washington in June.

Referring to Mr. Obama’s pledge that he would not allow Iran to acquire nuclear weapons, Mr. Peres said Thursday: “I am convinced this is an American interest. I am convinced he recognizes the American interest and he isn’t saying this just to keep us happy. I have no doubt about it, after having had talks with him.”

Iran insists that its nuclear program is for purely peaceful purposes.

The internal Israeli debate on Iran, once conducted in whispers, has become increasingly shrill.

Shaul Mofaz, a former defense minister and military chief of staff who now leads the opposition in Parliament, accused Mr. Netanyahu on Thursday of “sowing panic” over Iran, of being led by Mr. Barak and of following a “dangerous and irresponsible policy.”

Mr. Barak acknowledged in Parliament that there were differences over how to deal with Iran, but insisted that the issue was being debated here more thoroughly than any other he could remember.

In a separate development, a firebomb was hurled at a Palestinian taxi in the West Bank on Thursday evening, causing it to catch fire and wounding six people. Israeli military officials said there were indications that Israeli civilians were behind the attack, which occurred near the Jewish settlement of Bat Ayin, south of Jerusalem.

Palestinian medics said that the wounded were all members of one family, among them the driver and two young children.

Mr. Netanyahu strongly condemned the attack in a statement, pledging to make every effort to catch the perpetrators and bring them to justice.