"In the past months we saw Iranian attempts to attack Israelis in Thailand, India, Kenya and Cyprus," Netanyahu was quoted by Haaretz as saying. "Exactly 18 years after the attack on a Jewish community center in Argentina, the Iranian terror continues to hurt innocent people."
Netanyahu said Wednesday's attack in Bulgaria is part of "an Iranian terror offensive that is spreading throughout the world," and Israel will have a "strong response."
The Bulgarian Interior Ministry indicated the attack, near the arrival terminal at the Burgas airport, happened shortly after the tourists landed in Bulgaria at 4:45 p.m.
The Sofia News Agency reported the Burgas mayor as saying nine people were missing and 33 injured in the blast.
Mayor Dimitar Nikolov told bTV "a very strong explosive" was "deliberately placed or brought into the baggage compartment of the bus."
The Jerusalem Post said six people were killed at the scene and a seventh died at a hospital. Israeli Foreign Minister Avigdor Lieberman spoke with Bulgarian Foreign Minister Nikolay Mladenov, who was en route to the scene, the Post said.
The Post cited Bulgarian media reports that said Israel requested Bulgarian authorities increase security for Israeli citizens after a suspicious package was found on a bus carrying Israeli tourists from Turkey to Bulgaria in January.
U.S. President Barack Obama issued a statement from the White House, saying: "I strongly condemn today's barbaric terrorist attack on Israelis in Bulgaria. My thoughts and prayers are with the families of those killed and injured, and with the people of Israel, Bulgaria, and any other nation whose citizens were harmed in this awful event. ...
"The United States will stand with our allies, and provide whatever assistance is necessary to identify and bring to justice the perpetrators of this attack. As Israel has tragically once more been a target of terrorism, the United States reaffirms our unshakable commitment to Israel's security, and our deep friendship and solidarity with the Israeli people."