By Elizabeth Blunt BBC News, Nigeria

Human trafficking is one of Nigeria's concerns

A statement said this was necessary because of the increase in cross-border crime.

The surprise move closes Nigeria's western border with immediate effect.

A government statement said the action was being taken because of increasing crime such as smuggling and human trafficking.

The main border crossing into Benin is not far from Nigeria's commercial capital Lagos and it normally seethes with travellers and traders from Benin, Togo, Ghana and beyond.

The move... flies in the face of west Africa-wide agreements guaranteeing free movement of goods and people

Whenever Nigeria has imposed protectionist policies banning various imports, this has been the preferred way in for prohibited goods.

Imports at Benin's main port of Cotonou have risen sharply and its border area has become one vast market supplying Nigerian traders.

Cheap petrol

After a period of deregulation, Nigeria now appears to be moving back towards a protectionist regime.

Imports of sugar, sweets, beer, school exercise books and envelopes were banned from last month, although foreign brands are still abundantly available.

This same smuggling route can also be used for more sinister imports, like guns and ammunition.

And, meanwhile, petrol flows in the opposite direction.

Despite a recent price increase, petrol in Nigeria at around 25 US cents a litre is still the cheapest in the region.

Nigeria exports crude oil, but at the moment it is having to import refined products and significant quantities leak out over the border to supply neighbouring countries.