Suspected Islamist militants killed six people at a national guard base and two stores selling firearms in the Kazakh industrial city of Aktobe on Sunday, the Interior Ministry said.

Four of the attackers were killed and seven were detained by police in a counterterrorism operation, ministry spokesman Almas Sadubayev said. Some remained at large, he added.

Sadubayev said police suspected that the attackers were “followers of radical, nontraditional religious movements,” a phrase used in Kazakhstan, a mostly Muslim nation, to describe Islamist militants.

In near-simultaneous attacks, the gunmen killed a clerk and a guard at one firearms store and wounded three police officers who arrived at the site. At the second firearms store, a customer was slain, and responding police officers killed three attackers.

A third group hijacked a bus and used it to ram the gate of a national guard base, where they killed three service members before guards and police killed one attacker.

Sadubayev did not say how many people were involved in the three attacks.

A resident of Aktobe who spoke on the condition that only his first name, Valery, be used, said he had seen armed police from his balcony and heard a few gunshots.

“They were telling children playing outside to run to their homes,” Valery said, adding that he had also seen low-flying helicopters.

He said he received a text message that a curfew was being imposed in the city.

Police shut down public transportation, malls and entertainment venues in the city after the attacks, which took place on the eve of the Muslim holy month of Ramadan.

Aktobe, about 60 miles from the Russian border, was the site of Kazakhstan’s first suicide bombing in 2011, when a local man detonated an explosive device inside the building of the state security service.

Kazakh authorities often announce detentions and trials of Islamist militants, but most of them are people who traveled or planned to travel to places such as Syria and Iraq. Violent clashes within the country are rare.

However, the plunge in the price of oil, Kazakhstan’s main export, has threatened political and social stability in the former Soviet Central Asian nation of 18 million.

Thousands of Kazakhs took part in street protests across the country in April and May that were triggered by a planned land reform but quickly became an expression of general discontent with the government of President Nursultan Nazarbayev, who has been in power for about 25 years.