Israel has blamed the blast on Iran and its proxy group Iranian-backed Hezbollah, a Lebanese Shiite Muslim guerrilla group, and threatened retaliation.
Iranian Foreign Ministry spokesman Ramin Mehmanparast said the charges are aimed at diverting world attention from Israel's role in the assassination of Iranian nuclear scientists.
Tehran claims Israel's Mossad spy agency has been behind the slayings of at least five nuclear scientists since 2010, as well as other clandestine operations such as planting powerful computer viruses.
"The Zionist regime, which had a direct role in the assassination of our country's nuclear scientists, is leveling baseless accusations to divert global attention to its own terrorist nature," the official IRNA news agency quoted Mehmanparast as saying.
Iran's state TV also called the claims "ridiculous" and "sensational" in a commentary on its website. It said Israel was trying to discredit Iran and its allies such as Syria.
The attack occurred Wednesday shortly after the Israelis boarded a bus outside the airport in the Black Sea resort town of Burgas, a popular destination for Israeli tourists about 400 kilometers (250 miles) east of the capital, Sofia. Seven people - five Israelis, the Bulgarian driver and the bomber - died in the blast.
The violence comes against the broader backdrop of the international standoff with Iran over its nuclear program. Israel, accusing Iran of developing atomic weapons, has repeatedly hinted it is prepared to strike Iranian nuclear targets if Tehran does not curb its suspect program. Iran denies it is trying to develop nuclear weapons.
