DAKAR, Senegal — Islamists who control northern Mali have publicly amputated the hand of a man they accused of robbery, continuing an increasingly harsh application of what the vast region’s new masters consider sacred law.

The amputation took place Wednesday morning in the small town of Ansongo, just downriver from the provincial capital, Gao, which is under the rule of an Islamist group, splintered off from Al Qaeda, called the Movement for Oneness and Jihad in West Africa, or Mujao. It was confirmed by a Mujao spokesman in Gao in a telephone interview, and by the Malian government in a statement later from Bamako, the capital.

A witness in Ansongo said that the accused man’s hand was “placed on a sort of table,” in front of dozens of spectators, in the town’s main square. Then, “a gentleman with a sort of cutlass” — the witness described him as “an Arab” — swung hard, and sliced off the man’s hand, the witness said. “He cut it. There was a lot of blood.”

“He held up the man’s hand for the people, like a sort of trophy,” the witness, a local teacher, said Thursday in a telephone interview from Ansongo. “He said, ‘God is great.’ It was barbaric.”