LAGOS, Nigeria (AP) — All schools and government offices in Nigeria's capital will close during a three-day international conference next week, according to a presidential order that follows two bomb attacks in three weeks that killed nearly 100 people in Abuja.

A statement Friday night said the measure "is to ease the flow of traffic" during the May 7-9 World Economic Forum on Africa to which hundreds of international personalities, business and African leaders are invited. Chinese Premier Li Keqiang is the guest of honor.

The government has said it is deploying 6,000 police and troops to help secure the event, and President Goodluck Jonathan has assured delegates they will be safe.

Further indicating Nigeria's security threats, the U.S. Embassy warned Americans in an email Friday that extremists were planning "an unspecified attack" on a Sheraton hotel in Nigeria's commercial capital, Lagos.

The hotel chain has two locally owned franchises in the southwestern city of about 20 million people. A duty manager at the $350-a-night Sheraton in Ikeja suburb, near the international airport, said he was unaware of any threat. He spoke on condition of anonymity because he is not authorized to speak to reporters.

Explosions on April 14 and May 1 in Abuja, in the center of the country, are blamed on the Islamic extremists Boko Haram terrorist network that has targeted schools and slaughtered hundreds of students.

Militants of Boko Haram — the nickname means "Western education is sinful" — are holding some 276 teenage girls abducted from a northeastern school April 15.

In response to national outrage and protests at the failure to rescue the girls, Jonathan on Friday announced a that presidential committee headed by a retired general will mobilize people in the area of the mass abduction and other citizens "for a rescue strategy and operation" and to "articulate a framework for a multi-stakeholder action for the rescue of the missing girls."

Unverified reports this week that the militants are demanding ransoms for their release coincided with stories that some of the girls and young women — they are aged 15 to 18 — have been forced to "marry" their extremist abductors and some have been carried across borders into Chad and Cameroon.

The attacks and the prolonged captivity of the girls have gravely undermined confidence in Jonathan and his government as Nigeria prepares for February 2015 elections.

Nigeria is fighting a 5-year-old Islamic uprising by extremists whose stronghold is in the remote northeast but who are threatening attacks across Africa's biggest oil producer.