The president of Uzbekistan on Wednesday extended his condolences to President Trump and promised his country's assistance after an ­Uzbek immigrant driving a rental truck plowed down people on a Manhattan bike path Tuesday, killing eight and injuring 11.

Sayfullo Saipov, 29, is the main suspect in what authorities are calling a terrorist attack, one that casts a new spotlight on the tumultuous republic in Central Asia that has been a prominent source of fighters for the extremist Islamic State group.

Saipov’s case underscores the complications of trying to predict which immigrants are likely to commit acts of terrorism. Investigators in New York believe Saipov turned toward extremism only after he left the country and moved to the United States, according to Gov. Andrew M. Cuomo (D).

In a statement Wednesday, President Shavkat Mirziyoyev also offered condolences to families of the victims. Separately, the Uzbek Foreign Ministry said it is "determining the identity and citizenship" of the attacker, who was shot and arrested by police shortly after the assault.

Uzbekistan is one of five predominantly Muslim former Soviet republics in Central Asia that overnight became independent countries in 1991. Racked by poverty and corruption and ruled by autocratic leaders, the region has seen a growth of conservative versions of Islam and the recruitment of hundreds of militants to fight for the Islamic State.

Governments in these countries tightly regulate religious expression, censor literature and arbitrarily ban activities by any who oppose the ruling regimes. Human Rights Watch has documented the imprisonment and torture of thousands of Muslims for exercising their religious faith.

Mirziyoyev's predecessor, Islam Karimov, was a former Communist Party apparatchik who ruled Uzbekistan as his personal fiefdom while reaping political and economic benefits from the U.S. war in Afghanistan. 

To maintain his rule, Karimov fostered Uzbek nationalism, filled prisons with political opponents and targeted independent religious groups, justifying mass arrests of Muslims as necessary in the struggle against Islamist radicalism.

Observers believe that such oppression, in fact, encouraged the growth of radicalism among some Muslims, who then went on to join the ranks of homegrown groups, such as the Islamic Movement of Uzbekistan, as well as international militant organizations such as the Islamic State.

A recent report by the International Crisis Group, a nongovernmental organization that monitors conflict, estimated that between 2,000 and 4,000 people in Central Asia have become radicalized.

The nexus of Islamist radicalism in Central Asia is the Ferghana Valley, where Uzbekistan borders Kyrgyzstan and Tajikistan.

“Lack of opportunities and access to good education among youth, a poor labor market, conflict tensions among ethnic groups, political turbulence, and widespread corruption in the government system leave a large part of the population vulnerable and marginalized,” Akylai Karimova, who runs a U.N.-funded project to reduce radicalism among young people in the Ferghana Valley city of Osh, Kyrgyzstan, told The Washington Post in an interview earlier this year. “These, in turn, become a perfect base for radical elements to spread among them.”

Russian President Vladi­mir Putin, who has faced a radical Islamist rebellion in the North Caucasus region of his own country, recently estimated that several thousand people have left Central Asia to join the Islamic State in the Middle East.

Putin’s spokesman on Wednesday also offered condolences for the “tragic, inhumane attack.”

Russia arrested and charged a number of ethnic Uzbeks with ties to Kyrgyzstan and Uzbekistan in the investigation of the bombing of a St. Petersburg subway train, which killed 16 people.

While Trump on Tuesday cited the New York City attack as cause to tighten immigration to the United States, authorities said Saipov had apparently been radicalized since coming to the United States.

Terrorism experts say people who have carried out attacks in Russia and the United States later claimed by the Islamic State are more often radicalized while living there, rather than being foreign fighters sent on a mission.

The Boston Marathon bombing was carried out by two brothers with ethnic roots in Russia’s restive North Caucasus region who, investigators determined, became radicalized while living in the United States.

“The old idea is that terrorist organizations are trying to infiltrate the United States, and this is just simply out of date,” said Robert Pape, director of the Chicago Project on Security and Terrorism at the University of Chicago. “This doesn’t capture [that] ISIS is trying to radicalize people who are already living here.” ISIS is an acronym for the Islamic State.

“ISIS is radicalizing people who have been living in the community for a long time,” Pape said. “ISIS is using propaganda from overseas trying to inspire people who are already in the country. It’s a myth that we’re just simply being attacked by forces that come from abroad.”

Read more: