A Swiss missionary held by Islamist extremists in Mali for the last four years has reportedly been killed. 

Beatrice Stockli was abducted from her home in Mali in 2016.  A video released by her kidnappers soon after said: "Beatrice Stockli is a Swiss nun who declared war against Islam in her attempt to Christianize Muslims."

The kidnappers claimed to be from the Algeria-based militant group, al-Qaeda in the Islamic Maghreb.

News of her death was relayed by recently released French charity worker Sophie Pétronin, 75, who was also abducted by jihadists in 2016.

Pétronin said Stockli was shot dead by her kidnappers around a month ago when she refused to move to another location. 

The charity worker said they were often moved around to evade Malian and French soldiers. 

Swiss Federal Councillor Ignazio Cassis confirmed Stockli's death in a statement. 

"It was with great sadness that I learned of the death of our fellow citizen," he said. "I condemn this cruel act and express my deepest sympathy to the relatives."

The Swiss foreign office (FDFA) said it had "repeatedly" lobbied the Malian authorities for Stockli's release. Following news of her death, the FDFA said it was making every effort to locate her remains.

"Switzerland will make every effort to preserve the remains of the Swiss hostage. To this end, the FDFA will also approach the transition government in Mali," it said.