Seven people were killed, five of them Israelis, and 34 people were injured, two of them seriously, when a blast tore through a bus shuttling Israeli tourists in the terminal of Sarafovo Airport.
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Iran officially condemned the attack. Tehran's Foreign Ministry issued a statement saying that, "The Islamic Republic of Iran, which is the biggest victim of terrorism, believes that endangering innocent lives is… an inhumane act and we strongly condemned it.
"Iran's position is to condemn all terrorist acts in the world," the statement added.
Israel and Bulgaria have launched a joint investigation into the terror attack, with collaboration from the FBI and CIA.
Commenting on Wednesday's attack, Netanyahu said: "All the signs are pointing to Iran. The murderous Iranian terror continues to target innocent people. Iranian terror is spreading worldwide."
Defense Minister Ehud Barak added that Israel's security forces "will act to track down the masterminds behind this act of terrorism."
The Iranian website described the Israeli charges as attempts to discredit Iran and its allies such as Syria.
The bombing is the latest in a string of attacks and plots around the world that Israel has blamed on Iran.
Hezbollah, which is seen as Iran's proxy in Lebanon, has also denied any connection to the attack.
AP and AFP contributed to this report
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