Marguerite Gnakade, sister-in-law to the west African nation's leader Faure Gnassingbe, called for his resignation during a period of rare anti-government protests.

"She was arrested for serious acts, including her recent public appearance inciting the military to rebellion," a police source told AFP.

Local media outlet Republic of Togo, citing security sources, reported that Gnakade was "being questioned by the competent authorities".

Gnakade, who was minister from 2020 to 2022, had published several opinion articles in recent months critical of the government of Gnassingbe, who has been in power since 2005.

"Keeping Faure Gnassingbe in power any longer will change nothing. He must responsibly resign to make way for a peaceful, inclusive, and national transition, aimed at rebuilding our country," she wrote last month.

The "Don't Touch my Constitution" organisation of opposition parties and civil society groups said the arrest was carried out "without a warrant by a large number of hooded security forces".

"Once again, this is an abuse of power that characterises the regime's retrograde practices. The aim is to silence a dissenting voice," the group said in a statement.

"The Togolese people no longer accept this governance of terror," they added.

On August 30, Gnakade supported a street protest called by bloggers and artists, before being stopped by security forces.

In late June, protesters staged several days of rallies during which at least seven people were killed, according to civil society groups.

Protesters demonstrated against the arrests of government critics, rising electricity prices and a constitutional revision that allowed Gnassingbe, 59, to strengthen his grip on power.