Nigeria cracks down before World Economic Forum event
Nigerian security forces have detained several people in Abuja over recent bomb attacks, days before a World Economic Forum event in the capital.
Most of those held were said to be foreign, but no details were announced.
Schools and government offices are to close during the WEF event, which will be attended by the presidents of Rwanda, Senegal and Kenya as well as Chinese Premier Li Keqiang.
The government is under pressure to tackle widespread unrest.
An explosion late on Thursday killed 19 people, two weeks after a nearby bombing left 75 dead.
No group has said it carried out the attacks, but Islamist militant group Boko Haram is being blamed.
A spokesman for the Ministry of Defence said those detained on Saturday were being interrogated and had provided "useful information."
Boko Haram is also believed to be behind the kidnapping of more than 200 teenage girls from their school in Borno state in north-eastern Nigeria more than a fortnight ago.
President Goodluck Jonathan is due to give a national address on Sunday after criticism of his handling of Islamic militants.
Boko Haram has staged a wave of attacks in northern Nigeria in recent years, with an estimated 1,500 killed in the violence and subsequent security crackdown this year alone.
But recent bomb attacks in Abuja, including one on 14 April that Boko Haram admitted to, have raised fears that the militants could be trying to expand their area of operation.
On Saturday the US warned its citizens of a plan to attack one of two Sheraton hotels near Lagos, Nigeria's main commercial hub.
In a statement on its website, the state department said those behind the plot were "groups associated with terrorism", but gave no further details.
President Goodluck Jonathan's government says 5,000 police and soldiers will be deployed for the WEF on Africa, which begins on Wednesday.
The official reason for closing all schools and government offices in the capital is to ensure traffic flows smoothly.
But the BBC's Will Ross in Abuja says security concerns are also a likely reason, with fewer vehicles on the roads enabling stricter searches and cutting potential targets for further bomb attacks.
The government minister said the security measures were aimed at calming nerves but told Nigerian media the focus on returning the abducted girls to their families was "much more important".