An opposition leader in Rwanda has said the murder this week of a senior official in her party was an attempt to intimidate those trying to enter politics to challenge the veteran president, Paul Kagame.

Sylidio Dusabumuremyi, the national coordinator of the FDU-Inkingi party, was stabbed to death at his workplace, a canteen at a health centre in southern Rwanda, by two unidentified attackers who arrived by motorbike.

Victoire Ingabire, the party’s leader, said Monday’s attack was aimed at preventing her party from winning official recognition.

“They want to prevent me from creating an opposition party … This killing has no other implications other than intimidating Rwandans from participating in politics of their country,” she said.

Kagame won a landslide victory in 2017 elections, securing a third term in office with 99% of the vote.

The 61-year-old has garnered international praise for the stability and economic development he has achieved in Rwanda since the 1994 genocide, when an estimated 800,000 people were killed, but he has also been accused of running an authoritarian, one-party state.

Paul Kagame speaking at the United Nations general assembly this week. Photograph: Johannes Eisele/AFP/Getty Images

Authorities in Rwanda said they were investigating the attack and two people had been arrested.

“Investigations continue to arrest other suspects and establish the motive behind the murder,” the Rwanda investigation bureau said in a statement on social media.

The murder was the latest in a series of attacks that have targeted opposition figures inside and outside Rwanda.

Amnesty International said the killing of Dusabumuremyi followed numerous suspicious attacks and was “extremely alarming”.

Ingabire, 50, returned to Rwanda to launch an opposition political movement in 2010 after 16 years exile in the Netherlands, but was jailed before she could contest the election. She then served much of a 15-year sentence on terrorism charges, which she says were politically motivated.

Speaking to reporters in Kigali as she arrived at a hearing in the case of nine other people from her party who face terrorism-related charges, Ingabire called on security services to “do something about those killings and protect the opposition members as all Rwandans”.

Dusabumuremyi was at least the second of Ingabire’s aides to be killed this year.

On 15 July 2019, Eugène Ndereyimana, another member of FDU-Inkingi, was reported missing by his colleagues when he failed to show up for a meeting in Nyagatare in Rwanda’s Eastern province, and in March the body of Ingabire’s spokesman was found on the edge of the Gishwati forest in March after he disappeared while travelling to visit his parents.

Last year Boniface Twagirimana, FDU-Inkingi’s vice-president, was reported to have escaped from Mpanga prison, a maximum-security jail in the southern Nyanza district, but has not been seen since. Human rights campaigners say the circumstances of his alleged escape suggest he may have been abducted and killed.

Kagame’s government came under international scrutiny in 2014 when the president’s former spy chief Patrick Karegeya was found strangled in a luxury hotel in Johannesburg on New Year’s Day.

Karegeya took charge of Rwanda’s foreign intelligence services for a decade, until he fell into disgrace. He was jailed twice, in 2005 and 2006.

South African prosecutors said they found “close links” between the murder suspects and Kagame’s government. Rwanda has always denied the allegations.

South Africa has asked Rwanda to extradite two men suspected of murdering Karegeya, in a move likely to sour relations between the two countries.

Protesters seen earlier this year outside the Rwandan embassy in Pretoria, South Africa, calling for an investigation into the killing of Patrick Karegeya. Photograph: Alexander Joe/AFP/Getty Images

Kagame forcefully denied any human rights abuses in Rwanda earlier this year, calling criticism “absolute rubbish” and “ridiculous”.

“You [in Europe] really need to stop this superiority complex nonsense about human rights,” Kagame told France24. “You think you’re the only ones who respect human rights, and all others it’s about violating human rights. No, we have fought for human rights and freedoms of our people much better, and more than anyone including you people who keep talking about this nonsense.”

In September last year, 2,000 prisoners were released, including Ingabire. Human rights organisations welcomed this, saying it showed that “Rwanda may be turning a new leaf”, but said the arrests, executions, disappearances and torture would have to end to prove that the change was meaningful.

Despite some discontent over unemployment and other domestic issues, and a controversial reputation overseas, Kagame appears to be genuinely popular in Rwanda.

Some observers have questioned the reliability of the economic statistics showing growth. Others allege that increasing cronyism could undermine economic progress.