— Israeli officials maintained Thursday that Iran was behind a suicide bombing that killed five Israeli tourists in Bulgaria and vowed to settle the score, but indicated that retaliation was unlikely to take the form of a military strike on Iran.

Prime Minister Benjamin Netanyahu said the Wednesday attack was “part of a global campaign of terror carried out by Iran and Hezbollah,” a Lebanese militia that receives Iranian support. Netanyahu’s statement followed a string of similar comments by other senior Israeli officials and President Shimon Peres, who pledged to “take action in every terror nest.”

Israel offered no concrete evidence tying the bombing to Iran, and Bulgarian officials cautioned that it was too early to attribute responsibility.

Even as it blamed Iran, Israel, which has threatened military action to halt Iran’s alleged nuclear weapons program, also signaled that its response would not be overt.

“No option has been ruled out. But the last thing that we should do is shoot from the hip. It is better to keep our cool and use our judgment,” Israeli Deputy Foreign Minister Danny Ayalon told Israel Radio. Defense Minister Ehud Barak said Israel would “find those responsible, and those who dispatched them, and punish them.”

Israeli security analysts said the response is likely to be unseen, part of what is widely believed to be a clandestine, tit-for-tat cycle of attacks and assassinations between Israel and Iran. Because the bombing in Bulgaria, if carried out by Hezbollah, was at the “sub-state level,” Israel will probably respond in kind, said Yoram Schweitzer, who researches Iran and Hezbollah at the Institute for National Security Studies in Tel Aviv.

“The level of trying to prevent the Iranian nuclear program is a much higher and more intensive level of warfare,” Schweitzer said. “One can’t mix these two. If Israel is looking for a pretext, I’m not sure it will find it in this.”

Other analysts said that Israel, despite its threats, is unwilling to attack Iran without American backing. Asked about the possibility on Thursday, White House spokesman Jay Carney told reporters the United States believes that “the window for a peaceful resolution to this is still open and that the right approach is to continue to put pressure on Iran to live up to its international obligations and forsake its nuclear weapons ambitions.”

U.S. intelligence officials said it was “plausible” that Hezbollah carried out the attack but that analysts at the CIA and other agencies were still evaluating the intelligence surrounding the bombing and had not reached a conclusion.

“I think there’s a lot of people that assume, and have since day one, that this is Hezbollah,” said a senior U.S. official, who added that U.S. intelligence agencies had not reached such an assessment.

President Obama condemned the bombing on Thursday, saying during a campaign swing in Florida that it was “barbaric” and “ruthless.”

Bulgarian officials said the attack was carried out by a suicide bomber carrying a fake Michigan driver’s license, and they said they were analyzing DNA to identify him. They released video surveillance footage showing a rangy, long-haired man in his 30s, whose baseball cap and plaid shorts helped him blend easily into the crowd at the airport in the city of Burgas. The bombing took place in the parking lot as Israelis boarded a bus that was to take them to a hotel.

Iranian officials denied involvement Thursday.

Israeli diplomats and tourists have been targeted this year in a string of attacks and attempted attacks in a half-dozen countries, including Thailand and Kenya. Israel and the United States have tied the attacks to Iran and Hezbollah.

Iran has accused Israel of retaliating with assassinations of scientists involved in the Iranian nuclear program, which Israel views as an existential threat.

On Thursday, Israel seemed determined to use the attack to again focus world attention
on the dangers of Iran, which Netanyahu called the “premier terrorist-supporting state.” Galvanizing international pressure against Iran’s alleged nuclear weapons program has been one of Netanyahu’s key missions, and it is one widely perceived as successful. The United States and Europe have tightened sanctions against Iran, damaging its economy, and have stepped up talks with the country. Those diplomatic efforts have not yet borne fruit. Iran maintains that its uranium-enrichment program is for peaceful purposes.

Like the Bulgarians, U.S. officials declined to cast blame for the bombing. Some Israeli analysts questioned Israel’s certainty about the perpetrator and said it might have been premature to name Iran and Hezbollah.

“As long as we do not have any solid information about it, it is better to wait,” said Danny Yatom, a former director of the Israeli spy agency Mossad.

Meir Javedanfar, an Iranian Israeli lecturer at Israel’s Herzliya Interdisciplinary Center, said the Bulgaria attack fit the recent pattern of plots by Iran and Hezbollah against Israelis abroad. But it was also unusually brazen, he said. If Iran was behind the attack, Javedanfar said, “the Ayatollah Khomeini may have committed one of the biggest mistakes of his recent career. It’s one thing to kill Israelis. It’s another to kill them on E.U. soil. . . . Then the idea of the E.U. removing the oil sanctions anytime soon should be put on a shelf.”

Bulgaria’s press reported Thursday that the suicide bomber was a Swedish national captured in Afghanistan in 2001 and then detained for two years at the U.S. military prison at Guantanamo Bay, Cuba — an assertion that, if true, could indicate an al-Qaeda link to the attack. Swedish officials quickly denied the report.

An attack by al-Qaeda on Israelis would be unusual, but not unprecedented. The terror organization asserted responsibility for a deadly dual assault on an Israeli jet and
Israeli-owned hotel in Mombasa, Kenya, in 2002.

On Thursday, Israeli military jets that had flown to Bulgaria returned with more than 30 Israelis who were wounded in the bombing and the remains of the five tourists who were killed. Their funerals are scheduled to take place Friday.

Greg Miller in Washington contributed to this report.