LIBREVILLE: The security forces in Chad have brutally stifled dissent in the run-up to presidential elections this weekend, banning demonstrations, beating up protesters and carrying out arbitrary arrests, Human Rights Watch (HRW) said on Thursday.

The country's president, Idriss Deby Itno, a career soldier who seized power in 1990, is bidding for a sixth term in office.

"Chad's security forces have ruthlessly cracked down on protesters and the political opposition... harming Chadians' right to freely choose their elected representatives," HRW said in a report issued ahead of the vote Sunday.

Four peaceful demonstrations were dispersed by teargas in February and March and at least 112 opposition members and civil society activists were arbitrarily detained, HRW said.

"Witnesses described how security force members beat protesters with whips, sticks, and batons; pulled a wounded person out of a car and beat other passengers; arbitrarily arrested scores of people, and, in the attack on the home of an opposition leader, killed his mother," it said.

"One protester said he was subjected to electric shocks while in detention."

The rights watchdog said its reports were based on phone interviews with two dozen individuals, as well as analysis of videos and photographs.

In response to the accusations, Justice Minister Djimet Arabi told HRW that the security forces had acted with "professionalism" and banned protests had "sometimes led to violence and public disorder".

Deby is frontrunner in the two-round poll whose initial field of challengers has been whittled down from 16 to six.

Seven candidates have been rejected by the Supreme Court and three have withdrawn, including longtime opposition politician Saleh Kebzabo, who quit in protest over violence by the security forces.

On February 28, police and troops carried out a raid on the home of a prominent would-be candidate, Yaya Dillo Djerou.

His 80-year-old mother was among at least three people killed, and Yaya Dillo went into hiding.

The authorities said Yaya Dillo had put up "armed resistance" to the security forces, sparking a fight, but witnesses rejected this account, HRW said.