Relatives of those killed in last year's massive Beirut port explosion have accused Lebanon's former prime minister Hassan Diab of “running away” from investigators after heading to the US on holiday despite a hearing scheduled for Monday.

Diab said he was visiting the US for four weeks, via Istanbul, to see his two sons who are studying medicine in America.

Lead investigative judge Tarek Bitar summoned Mr Diab for questioning on Monday but it is now unclear if and when Diab, who was prime minister at the time of the blast, will appear.

The investigation into the causes of the blast, which killed more than 200 people, has stalled since August 2020 with numerous top officials refusing to appear to answer questions. Families of the victims have vowed to maintain pressure on politicians and the judiciary to ensure there is justice.

“We think he is fleeing from the investigation and this is incriminating evidence against him,” Ibrahim Hoteit, a representative for the families, told The National via phone.

“We will ask the investigative judge to work on bringing him back, through Interpol for example.”

Hoteit lost his brother in the explosion and has led efforts to demand a fair investigation and to pressure officials into complying with the law.

Diab also failed to appear before the investigators when summoned on August 26.

Tatiana Hasrouty, whose father was killed in the blast, said Diab was shirking his responsibilities.

“Couldn't he postpone his flight for a week to be questioned in a crime that killed more than 200,” she said.

“It's quite clear that his plan is to leave, bearing no responsibility.”

Diab's office did not respond to requests for comment on his trip or his plans to appear before the probe.

Earlier this year Diab was charged, along with three former ministers and MPs, with negligence in relation to the explosion.

The blast devastated parts of the capital, injuring more than 6,500 people and leaving hundreds of thousands homeless.

Diab is the highest-ranking former official that Bitar has summoned.

The victims' families held protests this week to demand those summoned for questioning actually appear before the investigative judge.

Former army chief Jean Kahwaji appeared for questioning on Monday.

Former public works and transportation minister Youssef Fenianos is set to appear Today, but Hoteit said the judiciary had given him an excuse to avoid facing questions.

Fenianos appealed against being summoned, saying he should be tried before a special court for ministers and presidents.

“This is an imaginary court that exists only on paper. Since 1991 it has not prosecuted anyone,” Hoteit said, adding that the families planned to protest against the judiciary if they did not reject Fenianos' request.

Families of victims appealed again to the international community again on Wednesday calling for the establishment of an independent investigation into the causes of the blast.

Human Rights Watch has accused local authorities of failing to hold those responsible for the explosion to account.

“More than a year after the explosion, Lebanese leaders continue to obstruct, delay, and undermine the domestic investigation,” said Aya Majzoub, Lebanon researcher at Human Rights Watch.