The suicide bomber in last week's deadly attack on Israeli tourists in Bulgaria entered from neighboring Romania, spoke decent Russian and had a female companion, local media reported on Monday.

Citing investigators probing last Wednesday's bombing of a bus at Burgas airport that killed five Israeli tourists and the driver, television channel bTV said that the attacker was in the city of Varna for at least a day before the bombing.

An autopsy on a suicide bomber who killed five Israeli tourists and a bus driver in Bulgaria show he was different from an "Arab-looking" suspect cited by witnesses, a doctor said on Sunday.

Galina Mileva, who was involved in the post-mortem examination, told BNT television on Sunday that the man "had a white face, light eyes, and very thick brown hair. The facial bones were shattered in the explosion."

Bulgarian police along with the CIA, FBI and Interpol are struggling to identify a suicide bomber who killed six people, including five Israelis, as the United States said the attack bore the "hallmarks" of Hizbullah.

Investigators have released CCTV footage of the person they believe carried out Wednesday's attack at the airport of the Black Sea town of Burgas on a bus carrying Israeli holidaymakers, which also claimed the life of the Bulgarian driver.

The Pentagon said Friday there are signs that Hizbullah may have orchestrated a suicide bombing attack on Israeli tourists in Bulgaria this week.

"The attack does bear some of the hallmarks of Hizbullah but we're not in a position to make any final determination on who was responsible," Pentagon press secretary George Little told reporters.

Cypriot police said on Thursday they are beefing up security to protect Israeli interests following a suicide bombing in Bulgaria that claimed six lives, including five Israeli tourists.

"Cyprus has taken additional measures at various places where there are Israeli interests in the light of the attack in Bulgaria," police spokesman Andreas Angelides told reporters.

Iran said on Thursday it strongly condemns "all terrorist acts" after a suicide bombing in Bulgaria killed six people including five Israelis.

"The Islamic republic, the biggest victim of terrorism, believes terrorism endangers the lives of innocents... is inhumane and so strongly condemns" it, Arabic-language television channel al-Alam cited foreign ministry spokesman Ramin Mehmanparast as saying.

Bulgarian investigators worked with the FBI and Interpol Thursday to identify the suicide attacker behind a deadly bombing on a bus carrying Israeli tourists, as Israeli Premier Benjamin Netanyahu said the attack "was perpetrated by Hizbullah" and Iran denied involvement.

The attack "was perpetrated by Hizbullah, Iran's leading terrorist proxy," said Netanyahu, describing the Lebanese group as "the long arm of Iran."

Bulgaria said Thursday a suicide bomber dressed as a tourist and with fake U.S. ID was behind an attack on Israelis on the Black Sea that killed seven people and left two in a coma.

U.S. President Barack Obama called the attack on a bus at Burgas airport on Wednesday, the deadliest against Israelis abroad since 2004, a "barbaric terrorist attack."

Israel accused Iran on Wednesday of being behind a deadly attack against Israeli tourists at an airport in Bulgaria, which Sofia said killed seven people and wounded more than 30 others.

There was no immediate confirmation of the nationalities of the casualties, but Israel's foreign ministry said the blast had targeted a bus carrying Israeli tourists who had just landed at the port city of Burgas on the Black Sea.

A 1,000-megawatt reactor at Bulgaria's Kozloduy nuclear plant was temporarily shut down early Saturday due to a turbo generator problem, but no rise in radioactivity was recorded, a statement said.

"Unit 6 of the Kozloduy plant was shut down by the turbo generator’s protection system," the plant said, adding: "No change in the level of radioactivity has been registered."