Plans and photographs of the home and office of Belgium’s prime minister, Charles Michel, have been found on a computer abandoned near a terrorist hideout in Brussels, according to Belgian sources.

The laptop was found in a bin near a flat in the Schaerbeek district that had been a makeshift bomb factory for the terrorists who killed 32 people and injured at least 340 in last week’s suicide bombings at Brussels airport and the city metro.

The find was first reported by several Belgian newspapers, including De Tijd and L’Echo, and has been confirmed by the Guardian. A well-placed source said: “We don’t know if they [the terrorists] were planning anything, but we do know they were investigating.” The laptop contained information about the prime minister’s official residence and office at 16 rue de la Loi in central Brussels, as well as photographs of the building taken from the street.

A spokesman for Michel said reinforced security measures had already been in place for several months.

The neoclassical building at Rue de la Loi is less than 6km away from the rundown Schaerbeek flat that served as the terrorists’ hideout. It was from this fifth-floor flat that the suicide bomber Ibrahim el-Bakraoui and two accomplices made the journey to Zaventem airport on 22 March to launch the attacks against unsuspecting travellers.

As news of the laptop find emerged, authorities revised down the number of people killed in the attacks: the Belgian crisis centre has announced that 32 people died, not 35 as stated earlier by health officials. “Deep checks” had shown that three people had been counted twice on two separate lists, the crisis centre said. The 32 dead comprised 17 Belgians and 15 foreigners, from countries including the UK, US, China, India, Italy, the Netherlands, Spain and Germany. The three suicide bombers – the Bakraoui brothers and Najim Laachraoui – are not included in the tally of the dead.

One week after the attacks, Brussels remains in a tense mood, with the airport and several metro stations still closed. On Wednesday, city officials announced that a demonstration by far-right protesters against Islamism had been banned. Génération Identitaire, a French far-right group, had been planning a march in Molenbeek with the rallying call “expel the Islamists” on Saturday afternoon, but the local authority has taken out a police order banning any public meeting on that day.

Françoise Schepmans, Molenbeek’s mayor, said she did not often take such decisions. “When we struggle against extremism, we are against all extremisms. It is out of the question to let people who are crazy with rage express themselves,” she told Le Soir. She warned that police would take action against anyone flouting the ban. Molenbeek has struggled to shake off its reputation as a hotbed for extremists, even before the Paris attacks suspect Salah Abdeslam was caught hiding there.