Burgas, Bulgaria (CNN) -- Investigators in Bulgaria are working around the clock to identify the man suspected of killing five Israeli tourists and their bus driver in an airport suicide bombing, the country's interior minister told reporters Friday.
Bulgarian Interior Minister Tsvetan Tsvetanov said police were trying to piece together the movements of the suspect, who was carrying a fake Michigan driver's license.
Investigators are also working to analyze the bomb, believed to have been located in a backpack placed Wednesday on the bus in a parking lot outside Burgas International Airport, Tsvetanov said.
Israel has said it suspects Iran or an Islamist militant group such as Hezbollah is behind the attack, a claim that has added to tension between Israel and Tehran. Iran, which has condemned the attack, has rejected Israel's claims.
The bodies of the five Israelis arrived Friday morning in Israel, said ZAKA, the volunteer emergency search-and-rescue organization that had gone to Bulgaria to recover them. The coffins, loaded onto a military plane at Burgas airport, were greeted with a ceremony on arrival at Ben Gurion airport outside Tel Aviv.
Israeli Tourism Minister Stas Misezhnikov said at the service: "This is a cruel, deliberate and well-orchestrated wave of terror. Its aim is to target Jews and Israelis, to take down human lives, to kill the freedom."
Among the victims was Kochava Shriki, who was on the bus with her husband and had learned that morning that she was pregnant, CNN affiliate Channel 10 reported. Childhood friends Maor Harush and Elior Priess also died, as did Itzik Kolongi and Amir Menashe, two men who were on holiday with their wives.
As Israelis grieved Friday, Bulgaria continued the hunt for clues as to who was responsible.
"At the moment, we are focused on finding the identity of the suicide bomber, and of course from the moment of the blast every single minute and every single hour of his being on the territory of Bulgaria," Tsvetanov said in a news conference broadcast on Bulgarian National TV.
The suspect was a foreigner who entered the country with fake identification documents and had been in Bulgaria for at least four days, he said.
Experts believe the attack was planned for the precise moment and place that it happened, he said, and they are certain from DNA analysis of body parts found at the scene that the attack was carried out by a suicide bomber.
But Tsvetanov said he was not excluding the possibility that a second person might have been involved.
Bulgarian authorities are working with their Israeli counterparts and international organizations like Interpol and Europol to identify the suspect, Tsvetanov said.
Authorities still don't know from where the suicide bomber came, where he stayed or what he did, Tsvetanov said.
A witness has said the suspect tried to rent a car from him but didn't have a proper driver's license, so was turned away, the minister said. FBI officials have said the man's Michigan license was fake.
Security footage aired by Bulgarian National TV shows the suspect, -- a white man with long hair and wearing khaki shorts, a baseball cap and sneakers -- looking relaxed as he walks among other travelers, carrying a backpack and a smaller bag.
In addition to the fatalities, the bombing wounded more than 30 Israeli tourists, some seriously. Israel's military flew 36 of the wounded back Thursday to Tel Aviv, where they were taken to Israeli hospitals.
The airport bus targeted by the attacker was to have taken about 47 passengers to a beach resort.
Bulgaria, whose Black Sea resorts are a popular destination for Israelis, has not speculated on who may have been responsible for the attack. Bulgaria received nearly 8.4 million visitors in 2010, the last year for which U.N. World Tourism Organization figures are available. The vast majority of the country's visitors that year, more than 8 million, came from Europe. About 25,000 visitors came from the Middle East.
U.S. President Barack Obama spoke with Bulgarian Prime Minister Boyko Borisov by phone on Friday. He condemned the "barbaric attack," gave his condolences and offered support for the investigation.
Bulgarian officials have sought to reassure those worried by what is an unusual attack in the nation, saying security has been boosted wherever needed.
Burgas airport has reopened and is functioning normally, Tsvetanov said, but access was restricted to passengers.
In a televised statement, Israeli Prime Minister Benjamin Netanyahu said Thursday that the attack was "perpetrated by Hezbollah, Iran's leading terrorist proxy," as part of a global campaign that has reached a dozen countries on five continents.
But he offered no evidence. Israel's U.S. Embassy said Wednesday that it had no proof that Iran was the instigator of the attack.
Pentagon Press Secretary George Little said Friday that the attack "does bear the hallmarks of Hezbollah." He refused to elaborate.
Netanyahu said Hezbollah and Iran have been trying to foment terrorism in countries that include Kenya, India and Cyprus, as well as in the United States, where an Iranian is accused of trying to kill the Saudi diplomat.
Iran's Foreign Ministry spokesman, Ramin Mehmanparast, said Israel was engaging in "baseless accusations against other countries in order to distract the attention of the international community from its terrorist activities being carried out throughout the world," according to a statement from the state-run IRNA news agency.
The Iranian Embassy in the Bulgarian capital of Sofia said earlier that Israeli suggestions that Tehran was involved in the attack were "unsubstantiated" and that the assertion was politically motivated.
CNN's Boriana Milanova, Guy Azriel, Atika Shubert and Laura Perez Maestro contributed to this report.