ABC News' Alexander Marquardt and Dragana Jovanovic report: Israeli Prime Minister Benjamin Netanyahu said he suspects Iran was behind a deadly explosion aboard a bus full of Israeli tourists in Bulgaria today.

"All the indications are that Iran is behind this deadly attack," the Israeli leader said, just hours after six people were killed and more than 30 others injured in a fireball aboard a bus at an airport in the eastern Bulgarian city of Burgas.

Foreign intelligence sources told ABC News the Bulgarian government had months ago received a warning from Israel and Russia that an attack may be imminent and, in response, security was stepped up at the Israeli embassy in Bulgaria's capital city of Sophia, more than 200 miles west of Burgas.

Investigators are trying to determine exactly how the bomb got on the bus in Burgas and have considered what one intelligence source told ABC News was a "remote possibility" it was slipped into a passenger's luggage and carried through from the last flight from Tel Aviv, Israel. The victims on the bus are believed to be from that flight, which was made up of 154 passengers - all Israeli except for one American and two Europeans.

Israeli security officials at the major airport in Tel Aviv, Ben Gurion Airport, earlier announced that future flights to Eastern Europe would be postponed while the government investigates the possibility of other planned attacks and whether there was even a chance that the bomb that eventually exploded in Bulgaria had somehow slipped through the Israeli airport's infamously intense security screening, intelligence officials said.

Netanyahu said the new explosion was just the latest in a "consistent pattern" of Iran-backed attacks targeting Israelis around the globe.

Over the weekend a Lebanese man was reportedly arrested in Cyprus for allegedly planning to attack Israeli targets there in a plot that Netanyahu also said was part of " Iranian terrorism."

Last month, two Iranian nationals were picked up in Kenya for allegedly plotting to attack U.S., Israeli, Saudi or British targets there, according to a report by The Associated Press. In recent months, agents suspected of plotting deadly attacks on behalf of Iran have also been arrested in the U.S., Azerbaijan and Thailand.

For its part, Iran has repeatedly blamed Israel for being behind the assassination of several of the country's top nuclear scientists in recent years.

In his statement, Netanyahu also noted that today marks the 18th anniversary of a bombing attack on a Jewish community center in Buenos Aires, Argentina - an attack the Israeli government blamed on Iran.

Israel's Minister of Defense, Ehud Barak, said it was "clearly" a terrorist attack "initiated probably by Hezbollah, Hamas, Islamic Jihad or another group under the terror auspices of either Iran or other radical Islamic groups."

"We are determined to identify who sent them, who perpetrated [the attack], and to settle the account," he said.

The White House said condemned "in the strongest possible terms" what it called an attack on innocent civilians, but Press Secretary Jay Carney said the White House does not know if it was terror-related.

Bulgaria is known as a popular tourist destination for Israelis, the AP reported.

ABC News' Richard Esposito, Lee Ferran and Dana Hughes contributed to this report.