* Politicians, relatives gather to remember 43 victims
* Feuding lawmakers suspend hostilities for the day
* Toll-road operator reiterates condolences (Updates with Genoa prosecutor)
By Francesca Landini
GENOA, Italy, Aug 14 (Reuters) - Grieving relatives asked bosses of Italy's biggest motorway operator to leave a ceremony on Wednesday honouring victims of last year's bridge collapse in Genoa that killed 43 people.
Infrastructure group Atlantia, which operated the viaduct that collapsed last Aug. 14 sending cars and trucks hurtling to the ground, has borne the brunt of nationwide outrage at the disaster.
The indignation bubbled to the surface again as political leaders - setting aside a government crisis in Rome - and relatives gathered in the northern port city to honour the victims on the anniversary.
As leaders took their seats for the ceremony, some mourners told Prime Minister Giuseppe Conte's staff they would leave if Atlantia officials remained, according to Giuseppe Matti, whose son Luigi was among those who died.
"It was insensitive to invite them," Matti told Reuters outside the damaged warehouse where the ceremony was held, near rubble left by the now-demolished bridge.
Approached by Conte's officials, the Atlantia delegation, including Chief Executive Giovanni Castellucci and Chairman Fabio Cerchiai, left to follow the ceremony remotely.
Some parts of the reinforced concrete viaduct had lacked proper maintenance for 25 years before it crumbled, according to a technical report commissioned by investigators, Genoa's top prosecutor Francesco Cozzi said after the ceremony.
Atlantia, controlled by the Benetton family famous for its retail clothing chain, denies accusations it neglected the bridge and declined to comment further after Cozzi's statement.
The executives left the ceremony to avoid it being "disturbed with any kind of controversy", the company said in a statement.
Atlantia says regular, state-supervised inspections had indicated the viaduct was safe, but it has struggled to repair its reputation.
The 5-Star Movement, one of two parties in Italy's governing coalition, has threatened to revoke Atlantia's licence to run motorways around the country.
Cozzi said he expected to complete his investigation into the disaster by the first half of next year.
"The investigation will tell whether (the lack of maintenance) was instrumental in causing the collapse," he told a news conference.
Atlantia shares fell after his comments, extending earlier losses to slide as much as 4% lower on the day.
The company published a full-page open letter in several national and local newspapers on Wednesday, reiterating condolences to the victims and their families.
Castellucci and Cerchiai are among dozens of company officials under investigation for suspected manslaughter over the collapse. They deny any wrongdoing.
Politicians suspended hostilities for the commemoration, which began with the names of the victims read aloud, moving some relatives to tears as Conte and Interior Minister Matteo Salvini stood among sombre-faced dignitaries.
Head of state Sergio Mattarella and 5-Star leader Luigi Di Maio also attended.
Conte addressed the hushed crowd at the site where a large section of the 1.2-kilometre (1,100-yard) motorway viaduct, built in the 1960s, crashed about 50 metres (165 feet) to the ground.
"We will never stop calling for justice for the victims," he said.
Pope Francis sent a message to the people of Genoa, saying their struggle to resign themselves to "a disaster that could have been avoided" was understandable.
The bridge collapse provided one of several points of conflict in the coalition that Salvini tore apart last week, a move that could lead to snap elections.
5-Star has accused Salvini's right-wing League of trying to protect the Benetton family and of resisting 5-Star attempts to revoke Atlantia's toll-road concession. Salvini denies this.
Asked after the ceremony if it was wrong to ask the Atlantia executives to leave, Salvini said: "In cases like this, relatives are always right. The mums, the dads, the children are always right. Their feelings are not debatable." (Additional reporting by Silvia Aloisi, Juliette Jabkhiro and Stefano Bernabei Writing by Isla Binnie Editing by Mark Bendeich, Janet Lawrence and Frances Kerry)