Nigeria Moves To Calm Investors After Attacks...

Officials Move to Bolster Security Around Abuja Just Weeks Before the Capital Hosts World Economic Forum Meeting

Workers cleaned up Tuesday at the site of a bomb blast that killed 75 people, many of them children and commuters, at a bus station in the Nigerian capital, Abuja. Agence France-Presse/Getty Images

ACCRA, GHANA (WALL STREET JOURNAL)—Hit by a wave of insurgent attacks, Nigeria raced Tuesday to secure the country's capital just weeks before it hosts a global showcase intended to trumpet its arrival into the club of big emerging economies.

Nigerian troops erected checkpoints on key roads and officials promised more police on the streets, one day after an explosion at a suburban Abuja bus station killed 75 people. Many of the dead were children and commuters on their way to school and work. 

Hours later, Islamist militants in the northeast drove trucks through the gates of a boarding school where teenage girls had been studying for final exams. Insurgents carried away more than 100 students at gunpoint, according to neighbors and a police official.

Last Thursday and Friday, the insurgency known as Boko Haram was blamed for attacks in northeastern villages that killed 217 people. The sect burned down four villages and shot civilians, according to Sen. Ahmed Zanna, the leading legislator from Borno state, which is the epicenter of Boko Haram's war to impose Quranic law across Africa's biggest economy. 

The display of carnage, which has become tragically commonplace in Nigeria's north, comes at a delicate moment for the government. The country's oil-rich economy just surpassed South Africa as the continent's largest, but the attacks are raising doubts among the very people Nigeria needs to fuel future growth: foreign investors.

Some are now saying they are still weighing participation in the three-day World Economic Forum meeting set to convene in Abuja on May 7.

"It depends on what's going to happen—whether or not it is an isolated event," said Paul Gomes, president of oil and gas advisory firm Constelor Investment Holdings. "I've learned to factor in the risk when it comes to Nigeria." 

On late Monday, the country's finance minister countered those misgivings, saying her government would station 6,000 police and soldiers along the leafy boulevards of Nigeria's capital. It "will be the largest security operation ever mounted in this country for an international summit," according to a statement from Minister Ngozi Okonjo-Iweala.

Spokesmen for the World Economic Forum didn't immediately respond to requests for comment.

Yvonne Ike, the chief executive of Renaissance Capital, West Africa, said curiosity among many investors in Nigeria's big fast-growing market will probably outweigh security concerns. Still, businesspeople will closely watch whether the Nigerian government can prevent another massive attack, according to the investment banker.

"If there isn't some sort of upscaling of security…then a lot of questions will come up," Ms. Ike said.

The attacks ahead of the economic forum show the dilemma troubling Nigeria. It is a nation battling insurgents with one hand of the government, and welcoming investors with the other. This month, the country of 174 million people became the largest economy in Africa—24th biggest in the world—capping a decade of growth that averaged 7.9% a year, according to the International Monetary Fund.

The forum was supposed to fête Nigeria's economic success, but it has raised questions about whether the country has the institutional strength to safeguard its capital from a few thousand insurgents.

Nigeria spends a fifth of its massive budget on security, and the government has more personnel under arms than South Africa. Its military hardware includes warships, fighter jets and cargo planes.

And yet a sect that trains in the woods has killed hundreds of people a week, largely in a bid to rid the country of English-language education.

Boko Haram fighters have killed more than 1,500 people so far this year in towns and villages scattered across the predominantly Muslim north, according to Amnesty International. Army leaders say they can't possibly protect so many hundreds of tiny towns from a sect so willing to gun down civilians. 

Monday's attack—a 15-minute drive from Nigeria's presidential palace—has now forced this government to confront the possibility, long feared in the west, that Boko Haram could turn its weaponry onto the foreign visitors eager to play a part in this country's growth.

On Tuesday, the U.S. State Department warned its citizens to stay away from Abuja's malls and hotels. The United Kingdom followed suit, asking its citizens to avoid the neighborhood where Monday's attack occurred.

"There is a high threat from terrorism in Nigeria," the U.K. advisory said.

The group has no track record of killing foreigners. But the group's leader, Abubakar Shekau, has goaded Western governments and leaders. 

In YouTube videos, he has laughed about the $7 million bounty for his arrest offered by the U.S. State Department. He has cursed Israeli Prime Minister Benjamin Netanyahu, U.N. Secretary General Ban Ki-moon, and even the late British Prime Minister Margaret Thatcher. In one video, his troops shoot rifles at scraps of paper labeled "Obama" and "Kansas."

Last month he added another target, declaring: " Queen Elizabeth, you are in trouble."

Write to Drew Hinshaw at drew.hinshaw@wsj.com