No opposition party claimed responsibility for the blockades, in which tree trunks were used to sever main roads, but an AFP correspondent reported that they were thought to have been erected by young people opposed to the president.

"It started around 4:00 am (0100 GMT) and lasted almost three hours, we heard gunshots," said a resident who spoke to AFP by telephone and declined to be named.

Anjouan Island governor Abdou Salami Abdou, member of the opposition Juwa party, confirmed the incidents.

"This has been ongoing since this morning, there is shooting everywhere," he said by phone.

There were no reports of any fatalities.

The leading opposition figures targeted in the crackdown include former president Abdallah Sambi, who has been charged with corruption. He is the head of the opposition Juwa party and is originally from Anjouan.

Assoumani increased his powers following a July referendum on constitutional changes boycotted by the opposition in which he scored 92.74 percent.

The amendments will mean that Assoumani, who previously came to power in a military coup and was elected in 2016, will be able to run for two terms.

He has indicated that he hopes to stage polls next year which would allow him to reset his term limits and theoretically rule until 2029.

His critics have accused him of a "dictatorial power grab".