Abuja - Kidnappers in northwest Nigeria seized a diplomat from Sierra Leone on Friday and are demanding a $40m ransom, that country's information minister and Nigerian workers at the embassy said.Deputy High Commissioner Nelson Williams was on his way to a military graduation in Kano state when he was kidnapped, Information Minister Mohamed Bangura announced from the capital, Freetown.The minister did not mention a ransom demand. But the embassy workers said the kidnappers almost immediately contacted the embassy to demand $40m for Williams' safe return.They said he was taken at gunpoint from his vehicle on the highway between Abuja, the capital in central Nigeria, and Kaduna city. Williams was travelling in convoy with an armed police escort, according to the workers, who insisted on speaking on condition of anonymity because they are not authorised to speak to reporters.Last week, three Australians, two Nigerians, a New Zealander and a South African were travelling in convoy with armed police officers when they were attacked by gunmen who killed a Nigerian driver and injured five of their hostages, all construction workers for an Australian company. They were released on Monday, but it was unclear if a ransom was paid.Most kidnappings for ransom in Nigeria do not result in fatalities, though a German construction worker was killed in southwestern Nigeria last year by gunmen who kidnapped a second German. He was later released.The highway travelled by Williams, a retired major general and former chief of the Sierra Leone army, is notorious. A Nigerian army officer was kidnapped there last week and returned to his family after they reportedly paid 500 000 naira ($1 800). A Nigerian colonel was kidnapped there three months ago, and his body was found dumped on the roadside days later.