Human Rights Watch on Friday urged Tunisia to put an end to what it called the "collective expulsions" of black African migrants to a desert area near the Libyan border.
Hundreds of migrants from sub-Saharan Africa have been left stranded in dire conditions in the south of Tunisia since being driven out of the port city of Sfax in the past week.
The rights group's statement comes against a backdrop of violence after the funeral of a 41-year-old Tunisian man who was stabbed to death in Sfax on Monday in a brawl between Tunisians and migrants.
Sfax, the North African country's second-largest city, is a departure point for many hoping to reach Europe by sea, often the Italian island of Lampedusa about 130 kilometres (80 miles) away.
"Tunisian security forces have collectively expelled several hundred Black African migrants and asylum seekers, including children and pregnant women, since July 2, to a remote, militarised buffer zone at the Tunisia-Libya border," HRW said.
"Many reported violence by authorities during arrest or expulsion," the New York-based watchdog said in its statement.
HRW's Lauren Seibert urged Tunisia's government to "halt collective expulsions and urgently enable humanitarian access to the African migrants and asylum seekers already expelled to a dangerous area".
The group said migrants it interviewed alleged "several people died or were killed at the border area" between Sunday and Wednesday, "some shot and others beaten" by Tunisian security forces.
- 'No time to waste' -
"They also said that Libyan men carrying machetes or other weapons had robbed some people and raped several women," HRW reported, adding it was unable to independently verify the accounts.
HRW called on the government in Tunis to "investigate and hold to account security forces implicated in abuses".
"African migrants and asylum seekers, including children, are desperate to get out of the dangerous border zone and find food, medical care, and safety," Seibert said. "There is no time to waste."
Tunisia has seen a rise in racially motivated attacks after President Kais Saied in February accused "hordes" of undocumented migrants of bringing violence and alleging a "criminal plot" to change the country's demographic make-up.
Some migrants forcibly taken to the desert told AFP by phone on Thursday that hundreds, including women and children, had been abandoned there and left destitute.
Video footage shared on Friday by an African association shows dozens of visibly exhausted people, including mothers with babies, sitting or lying on the sand in the desert by the Mediterranean near the border with Libya.
One begs for help, saying: "We have nothing to eat. How many days can we survive?"
In Sfax itself, hundreds of migrants gathered in a park on Friday to demand "peace and security", an AFP journalist said.
"I no longer have a place to live and I'm not safe any more. I just want to go home to Burkina Faso," said Abdelatif Farati, 18, who has been in Tunisia with his four brothers for four years.
"Black lives matter" read the slogan on pieces of cardboard held up as placards.
Some Tunisians have expressed solidarity with the migrants, providing food and medical help to those now living on the street after being chased from their homes.
On Friday, the head of Tunisia's main opposition coalition, Ahmed Nejib Chebbi, described the incidents as "a black page in our history".
"People are arrested just for the colour of their skin. This is a disgrace," Chebbi told AFP.