TUNIS — New evidence of the torture and deaths of detainees in police custody has emerged in Tunisia, indicating a rise in repression as the government has sought to crack down on terrorism, Amnesty International warned Wednesday.

Amnesty said it had collected evidence showing that at least six people had died in police custody since 2011 and that detainees, including women, were tortured and mistreated in prison last year after being accused of terrorist activities.

Tunisia was hit by several deadly terrorist attacks in 2015 — one in March killed 19 people at a museum, one in June killed 38 people at a beach resort, and another in November killed 12 members of the presidential guard — leading the government to impose a nightly curfew and a state of emergency. Tunisians make up one of the largest groups of foreign fighters for the Islamic State in Syria and Libya, and the security forces have increased raids and arrests in their efforts to thwart further attacks.

Amnesty International released its findings on the eve of the fifth anniversary of Tunisia’s popular uprising that overthrew the dictatorship of Zine el-Abidine Ben Ali, which was reviled for its human rights abuses. The group warned that Tunisia was in danger of slipping back to that “dark point.”