Rwanda has arrested prominent opposition leader Victoire Ingabire on charges of inciting public disorder and creating a criminal organisation, a state investigative agency said - a move one of her lawyers said was politically motivated.

Ingabire, who heads unregistered opposition party DALFA–Umurinzi, returned from exile to contest a presidential election in 2010, but was barred from standing after being accused of genocide denial.  

She was jailed two years later on charges related to conspiring to form an armed group and seeking to minimise the 1994 genocide - charges she denied - and freed in 2018.

She is now accused of "playing a role in creating a criminal organisation and engaging in acts that incite public disorder," the Rwanda Investigations Bureau said in a statement late on Thursday. It did not say when she would be charged in court. 

"For us, this is a continuation of a long process of intimidation and political harassment against Victoire and her supporters," Iain Edwards, one of Ingabire's international lawyers, told Reuters.

"It's to silence her and to warn others not to speak out against the government. People always fear for the lives of political opponents in Rwanda. I certainly fear for her life," he added.

Yolande Makolo, the government's spokesperson, did not immediately respond to a message and phone call requesting comment on the lawyer's statement.

Last year President Paul Kagame, in power for a quarter of a century, won re-election after securing 99.18% of the vote, according to the electoral body. 

Western and regional leaders have praised Kagame for transforming Rwanda from the ruins of the 1994 genocide into a thriving economy. Rights groups have accused him of abuses and of supporting rebels in neighbouring Democratic Republic of Congo, accusations that he denies.