Israeli security forces opened a massive manhunt for the individual and possible accomplices who planted a bomb on a bus in Bat Yam in an attempted terror attack Sunday.

A police sapper was lightly injured when the bomb exploded as he was trying to defuse it, minutes after all the passengers were let off the bus thanks to an alert passenger who spotted the suspicious bag containing the bomb, and promptly alerted the bus driver.

The explosion blew the windows out of the bus and charred the sides of the vehicle.

Police said it was the most serious attack inside Israel in more than a year, and urged the public to be on the alert for additional bombing attempts. Security forces set up roadblocks around the country and were searching cars heading into the West Bank.

The explosion came at a sensitive time in Mideast peace efforts. Israel and the Palestinians resumed talks last summer for the first time in nearly five years, and the US-brokered negotiations have made little visible progress. The explosion threatened to further poison what has become a tense and negative atmosphere.

The US government strongly condemned the bombing, saying “violent acts targeting civilians are deplorable.”

“We reaffirm our unshakable bond with Israel and our solidarity with the Israeli people,” read a State Department statement issued late Sunday.

President Shimon Peres phoned and thanked the bus driver and the passenger who discovered the explosive, saying their actions saved lives.

“The nation owes you a debt of gratitude and I would like to personally congratulate you for this act of bravery,” Peres told bus driver Michael Yoger.

Palestinian terror groups, meanwhile, praised Sunday’s attempted attack, but failed to take responsibility for the blast.

“We welcome the operation in Tel Aviv,” Hamas spokesperson Moshir al-Masri said in a message broadcast on Al Aqsa TV, the faction’s official station. “It comes as a response to all the actions the Zionists perpetrate daily.”

“The Jews need to pay a price — the Palestinians won’t stand by and not acknowledge [the Israeli actions]. The incident proves that opposition can reach deep into the Zionist territory,” he continued.

“This is the appropriate way to deal with Israel,” Ahmed al-Mudallal, a senior Islamic Jihad member, said in an interview on Al Aqsa TV. Al-Mudallal also threatened that the Palestinians are “on the verge” of resuming attacks against the “Zionist enemy.”

There was no public comment on the bombing from Fatah or the group’s armed winged, the al-Aqsa Martyrs Brigades.

The explosion badly damaged the Dan No. 240 bus, which was stopped at the time on the corners of Mivtza Sinai and Katznelson streets in Bat Yam on Sunday afternoon, which borders Tel Aviv on the south.

“A passenger alerted the driver about a suspicious bag located behind the back door of the bus,” a spokesperson for the Dan bus company said. “The driver stopped the bus and examined the bag. He saw electrical wires attached to the bag and ordered all passengers off the bus, leaving after them. He then called police sappers.”

Yoger deflected praise that he had saved the dozen or so passengers on the bus.

Michael Yoger (screen shot: Channel 2)

Michael Yoger (screen shot: Channel 2)

“I’m a hero? What hero? One of the passengers told me there’s a suspicious bag on the bus. I asked whose bag it is. When they told me it didn’t belong to anyone, I took the passengers off the bus. I stopped at the bus stop and the people got off, the police arrived at the scene and ten minutes later the bus exploded,” he said.

The passenger, later named as David Pappo, noticed the suspicious bag, opened it, and saw a pressure cooker with wires extending from it. He then alerted driver Yoger.

Initial reports said the bomb contained some five kilograms of explosives — enough to cause immense devastation.

The bomb that blew up a bus at Burgas airport in Bulgaria in 2012, killing five Israelis and a local driver, by way of comparison, contained three kilograms of explosives.

“At this point in time we are under the impression that the incident was nationalistically motivated. I urge the public to be aware and report any suspicious activity to the police,” Public Security Minister Yitzhak Aharonovitch said.