LAGOS, May 27 (Reuters) - Britain has advised its citizens against all travel to Nigeria's oil-producing Niger Delta because of the high risk of kidnapping and armed robbery, the government said on its Web site.

More than 180 foreign nationals, mostly oil workers, have been kidnapped in the region since the beginning of last year, including 30 Britons, it said. One British hostage was killed by the security forces last year in a botched attempt to free him. "We advise against all travel to the Niger Delta," the Foreign Office said, adding that it would be "reckless" to go there without taking professional security advice and using "fully protected" transport.

The warning was updated on May 25. The previous warning advised against travel only to the riverine areas of the vast wetlands region.

Hundreds of Britons still work in the region, which is home to Africa's largest oil industry, and Anglo-Dutch company Royal Dutch Shell <RDSa.L> is the nation's largest oil producer.

But thousands of foreign workers have left since the emergence of a new militant group in December 2005, whose attacks have closed about a quarter of Nigeria's oil output.

The militant group MEND, which says it is fighting for local control of the region's oil wealth, has ordered all oil workers to leave and vowed to halt exports.

But most of the kidnapping in the delta is by other armed groups seeking ransom. About 25 foreigners are currently being held captive.

AlertNet news is provided by