A Bulgarian court is due to deliver its verdict Monday in a trial over a deadly 2012 bus bomb attack on Israeli tourists at the country's Burgas airport.

The attack in July 2012 killed five Israelis including a pregnant woman, their Bulgarian bus driver and the man who carried the explosive, and left over 35 people injured.

It was the deadliest against Israelis abroad since 2004.

Prosecutors are demanding the maximum possible sentence -- life without parole -- for two suspects who fled Bulgaria and are being tried in absentia.

Bulgarian and Israeli authorities blamed the attack on the Lebanese Shiite movement Hezbollah, playing a part in a subsequent European Union decision to blacklist Hezbollah's military wing as a "terrorist" organisation.

A DNA analysis identified the bomber as 23-year-old Franco-Lebanese national Mohamad Hassan El-Husseini.

Airport CCTV footage showed him wandering inside the airport's arrivals hall with a backpack on his back shortly before the explosion that tore through a bus outside the terminal that was headed to Sunny Beach, a popular summer destination on the Black Sea.

According to witness accounts, he tried to put his backpack inside the luggage compartment of the bus full of Israelis when it exploded.

The tourists who were killed were all in their twenties, except for a pregnant 42-year-old woman.

Prosecutors were unable to determine if the explosive was triggered by the bomber or remotely detonated by one of two men, who had also helped him to assemble the explosive device.

The two were identified as Lebanese-Australian Meliad Farah, 31 at the time of the attack, and Lebanese-Canadian Hassan El Hajj Hassan, 24, and were charged in mid-2016 as El-Husseini's accomplices.

They were put on trial in absentia in January 2018 for a terrorist attack and manslaughter but were never tracked down.

According to an investigation into the bombing, they arrived in Bulgaria from Romania in June 2012, and left again on the evening after the attack.

- Hezbollah 'links' -

Prosecutor Evgenia Shtarkelova told reporters last week she "pleaded for the heaviest punishment because I consider that this terrorist act deserves to be punished in the heaviest possible way."

A public defender for Hassan, lawyer Zhanet Zhelyazkova, countered that evidence for her client's alleged complicity with the attack was "only circumstantial."

Shtarkelova however said that the nature of the explosive device, the fake US driver's licences used by the two men, their Lebanese descent and some family ties "link both defendants (...) and the attack to the terrorist organization Hezbollah."

The investigation into the attack found that the fake licences were made by the same printer at a university in Lebanon. It also said the suspects received money from people linked to Hezbollah.

In recent comments on the case, Bulgaria's chief prosecutor Ivan Geshev stressed that Hezbollah was behind the attack "in terms of logistics and financing".

The prosecution confirmed that it had no clue about the two men's whereabouts and that they are still sought on an Interpol red notice.

Judge Adelina Ivanova will deliver the verdict and hand down the sentences on Monday.

The court rulings still subject to appeal to a higher court.