A Nigerian court has ordered the extradition to Britain of a former senior finance ministry official accused of taking bribes in exchange for a contract to print bank notes, court documents showed Monday.

Emmanuel Okoyomon headed the Nigerian Security, Minting and Printing Company in 2006 when an Australian firm, Securency International, won a contract to produce low denomination polymer bank notes for Africa's most populous nation.  

Troops killed 28 suspected militants during a weekend operation in central Nigeria launched in response to an attack last month which saw six soldiers gruesomely murdered, the military said Monday.

The violence occurred on the border between Plateau and Taraba states, an area plagued by waves of sectarian violence seen as separate from Boko Haram, although the Islamist insurgents have claimed past attacks in the region.

Many of the women and girls rescued from Boko Haram are traumatized and showing signs of depression, with psychological counseling urgently needed as they recover in camps in northeast Nigeria, relief officials said Monday.

"For some of them, who are really showing signs of trauma, we need to make them realize that this is not the end of life," said Sa'ad Bello, the National Emergency Management Agency (NEMA) camp coordinator in Adamawa state.

Nigeria's military authorities on Sunday moved 275 women and children to a relief camp, days after rescuing them from Boko Haram's stronghold in the Sambisa forest, the state-run emergency agency said.

The freed hostages, among almost 700 women and children rescued from Boko Haram's clutches last week, had been traumatized and malnourished by their ordeal, the military said.

Nigerian troops have raided communities suspected of harbouring militiamen in central Plateau state, killing several people, a military spokesman said Sunday.

"Following frequent attacks on communities around the Plateau-Taraba border by some militiamen, we carried out an operation to flush out members of these murderous gangs," Captain Ikedichi Iweha of the special task force told Agence France Presse.

Nigeria troops have freed some 700 women and children from Boko Haram's Sambisa forest stronghold over the past week, but uncertainty remained on Saturday over the fate of 219 girls seized from their school in Chibok last year in a kidnapping that sparked global outrage.

In the latest rescue, "234 women and children were rescued through the Kawuri and Konduga end of Sambisa forest on Thursday," the defence headquarters said in a statement late Friday.

Niger authorities have urged people living on islands in Lake Chad to leave to avoid new attacks by Boko Haram, after an assault by the Islamists last weekend left at least 74 dead.

The weekend attack was the country's heaviest loss since it joined a regional offensive against the militants, and saw authorities declare three days of mourning from Wednesday.

Boko Haram hostages were held in atrocious conditions in the group's Sambisa Forest stronghold, Nigeria's military said on Thursday after nearly 500 women and girls were released this week.

"Whoever they may be, the important thing is that Nigerians held captive under very severe and inhuman conditions have been freed by our gallant troops," defense spokesman Chris Olukolade said.

Nigerian troops have rescued about 160 more hostages from Boko Haram's Sambisa Forest stronghold, the army said on Thursday, taking the total number liberated this week alone to nearly 500.

The numbers underlined the scale of the tactic of mass abduction used by the militants, who according to Amnesty International have seized about 2,000 women and girls since the start of last year.

Long tailbacks form at a bridge on the border between Chad and Cameroon while Chadian security forces, wary of deadly Boko Haram jihadists, screen all road users and their property.

"We're looking for weapons," a police officer explains at the Ngueuli bridge on the main road for imports to landlocked Chad, linking the capital N'Djamena to the far north of Cameroon.