A string of slayings claimed by radical Islamic groups has Bangladesh scrambling to contain what appears to be a rising tide of extremism, and it couldn't have come at a worse time — the country's fragile economic growth is faltering this year amid renewed political unrest.

The secular South Asian nation — traditionally moderate even if unstable at times — has repeatedly insisted it has religious radicalism in check and is maintaining peace among its 160 million people. That claim was severely tested this week after an Italian aid worker became the fifth person to be killed this year in attacks claimed by extremist groups.

A foreigner being gunned down in the country's capital is bad news for Bangladesh, whose economy is heavily reliant on a $25 billion garment industry that produces clothing and fashion wear for international brands including Zara, Benetton and Gap.

Hassan Shariar, a well-known political commentator and columnist, said even though the government won't acknowledge it, there clearly are pockets of radical Islam in the country.

"I don't know why intelligence (agencies) failed to understand that things are going out of control," he said. "It is clearly evident ... that they are failing to contain it with an iron hand."

Prime Minister Sheikh Hasina has been cracking down on radicals. Police have arrested dozens of suspected members of various hardline militant groups in recent years, including six that have been banned.

Still, the violence has continued. In February, when cleaver-wielding attackers killed an atheist writer and blogger, U.S. citizen Avijit Roy, authorities called it a random, isolated incident executed by religious fanatics.

Then it happened again. And again. And again.

In total, four bloggers and online activists — all critics of radical Islam — have been hacked to death with meat cleavers in daytime attacks. A hit list of 84 bloggers including many living in Europe and the United States has appeared online, allegedly posted by the Ansarullah Bangla Team — the same banned militant group that claimed responsibility or involvement in killing the bloggers.

Bangladesh intelligence officials have refused to confirm the list as a threat, saying it could not be independently verified, though they arrested two of the group's leaders in Dhaka last month.

Then on Monday, three motorcycle-riding assailants gunned down the Italian aid worker, Cesare Tavella, in the diplomatic quarter of Dhaka. The Sunni extremist group Islamic State claimed responsibility and vowed more such killings in Muslim-majority countries.

The government dismissed the IS claim, saying there was no evidence. It described the killing as an "isolated incident."

"There is no existence of the Islamic State here," Home Minister Asaduzzaman Khan said Tuesday.

That may actually be true. Still, the attacks present a serious challenge for Hasina, who rose to power in 2008 largely on promises she would crack down on the radicalism that has been evident since 2001, when the militant group Harkatul Jihad carried out a deadly bombing on New Year celebrations.

In 2004, a grenade attack by the same banned group killed 24 at an opposition rally, and in 2005 the group Jumatul Mujahedeen Bangladesh claimed to have set 500 small bombs that exploded in unison at more than 300 locations across the country.

Police raids on suspected militant hideouts have been a hallmark of Hasina's government. Some of the banned groups' leaders are behind bars and on trial, while Hasina's allies accuse the country's main Islamist political party, Jamaat-e-Islami, of backing the groups from a distance.

A court revoked the party's registration in 2013, effectively barring it from contesting elections. But it continues to be allied with the main opposition Bangladesh Nationalist Party of former Prime Minister Khaleda Zia.

Proscribing Jamaat-e-Islami has alienated many of its followers and "pushed Islamists to the edge," said Pinak Ranjan Chakravarty, a former Indian ambassador to Bangladesh.

He noted that Bangladesh also has a large number of madrasas, or Islamic schools, largely funded by Saudi Arabia and running their own religious curriculum. "The madrasas are radicalizing the youth, who can't find jobs after their Koranic studies and they are being recruited by extremist elements," he said.

Police have arrested about a dozen people suspected in the bloggers' murders, including two students of Islamic schools who said they were ordered by "someone" to carry out a killing in March, officials said. But authorities say they still do not know who that person is.

All four blogger attacks were claimed by groups connected to Ansarullah, which allegedly has ties to the al-Qaida branch launched in South Asia last year. But officials say the claims can't be verified.

Bangladesh is one of the world's poorest countries. Its 160 million people are packed in almost every corner of the low-lying delta nation, living uneasily at the edge of islands eroding or sinking into the Bay of Bengal. In recent years, the country has been trying to recover from a string of horrific accidents linked to its garment industry, one of the bright spots in its $572 billion economy, which is smaller than that of Chicago or Shanghai.

The industry grew about 14 percent between July 2013 and May 2014, and the overall economy has been growing by 6 percent annually for the last few years. The government had estimated that the economy would grow by 7.3 percent this year although the International Monetary Fund had a more conservative estimate of 6.4 percent. But in March the IMF revised its estimate to 6 percent, blaming repeated strikes, demonstrations and transportation blockades by the opposition since January. Some 120 people have died in the political unrest.

Against this backdrop, any escalation of Islamic extremism is certain to drag the economy down further by driving away foreign investors in the garment industry, who have already been complaining of a fall in orders.

The attacks have increased international concern, with the U.S., Canada and Britain issuing travel warnings to their citizens to be careful in Bangladesh. Australia's national cricket team canceled a tour in the country.

"Clearly, the Islamic groups have been active in Bangladesh for a long time. Now they seem to be very well organized in carrying out attacks on secular persons," said Zoya Hasan, a professor of politics at the Jawaharlal Nehru University in New Delhi, India.

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Associated Press writer Ashok Sharma in New Delhi contributed to this report.