Some 10,000 Nigeriens, fleeing mounting violence in neighbouring Nigeria, have crossed back into Niger over the past six months, officials said here Wednesday.

"Some 10,000 Nigeriens have crossed of their own accord" since the Islamist sect Boko Haram started to go on the rampage "and it isn't over yet", according to Boube Yaye, permanent secretary to the high council of Nigeriens abroad.

"And these figures don't take account of those who entered Niger without registering," he told Labari radio in Niamey.

Nigeria on Monday announced that some 11,000 people from neighbouring countries, including Chad and Niger, had been expelled over the past few months because of fear they might support Boko Haram.

The Boko Haram movement is based in Nigeria's north, near the country's border with Cameroon, Chad and Niger.

The sect has said it wants to create an Islamic state in Nigeria's deeply impoverished north.