U.S. President Barack Obama on Wednesday called Israeli Prime Minister Benjamin Netanyahu over a bomb attack on Israeli tourists in Bulgaria, pledging assistance to bring the perpetrators to justice.

The president offered his condolences and "strongly condemned this outrageous attack that killed and wounded innocent Israelis and Bulgarians, including Israeli children," the White House said in a statement.

"The president pledged to stand with Israel in this difficult time, and provide whatever assistance is necessary to identify and bring to justice the perpetrators," it noted, adding that Obama also "reaffirmed our unshakable commitment to Israel's security and our deep friendship and solidarity with the Israeli people."

Six Israelis were killed and more than 30 others injured earlier in the day, when a powerful blast ripped through a bus with Israeli tourists onboard at the Burgas airport in Bulgaria. Bulgarian Foreign Minister Nikolay Mladenov told his Israeli counterpart Avigdor Lieberman that the blast was caused by a bomb planted on the bus.

Netanyahu accused Iran of being behind the attack, warning that Israel will make a "strong response against Iranian terror." Tehran so far has not responded to the accusation.

Obama also denounced the "barbaric terrorist attack" in an earlier statement.