The detention of Karim Massimov was announced by the National Security Committee which he headed until he was fired this week by President Kassym-Jomart Tokayev as violent protests swept across the Central Asian nation.
Tokayev told Russian President Vladimir Putin in a "lengthy" phone call the situation in the country was stabilising, the Kremlin said.
It said Putin backed a proposal from Tokayev on the call to convene a video conference of leaders from the Collective Security Treaty Organisation (CSTO), under whose umbrella Russia and four other former Soviet republics have sent troops into Kazakhstan to help restore order.
Dozens of people have died, thousands have been detained and public buildings across Kazakhstan have been torched over the past week.
It's the worst violence experienced in the major oil and uranium producer since it became independent in the early 1990s as the Soviet Union collapsed.
Tokayev has ordered his troops to shoot to kill to put an end to what he has called attacks by bandits and terrorists.
He said on Friday the state had "slept through" instigators' preparations to launch attacks on the biggest city, Almaty, and across the country.Â
The arrest of Massimov indicated that moves against those deemed responsible are under way.
Apart from heading the intelligence agency that replaced the Soviet-era KGB, Massimov is a two-time ex-prime minister who worked closely with former president Nursultan Nazarbayev, the country's ruler for three decades until he turned over the presidency to Tokayev in 2019.
The demonstrations across the country began as a response to a fuel price hike but swelled into a broad movement against Tokayev's Russian-backed government and 81-year-old Nazarbayev.
Nazarbayev's family is widely believed to have retained influence in Nur-Sultan, the capital that bears his name.
