The brother and sister of the alleged suicide bomber who killed 36 people at Russia's busiest airport have been arrested for helping him, along with a third accomplice, Russian media said Wednesday.

Officials have said 20-year-old Magomed Yevloyev from Ingushetia, in the Muslim North Caucasus, was the bomber who struck Domodedovo airport on January 24.

His brother Akhmed, 16, and sister Fatima, 22, have been arrested, Itar-TASS quoted investigators as saying. Also detained was Akhmed Aushev, a resident of the same village, Ali-Yurt, southeast of Ingushetia's biggest city Nazran.

They helped Magomed Yevloyev prepare his bomb, the news agency quoted an unnamed source in Russia's investigative committee as saying.

Interfax said the trio were being sent to Moscow where they would be questioned.

The Ingush branch of the Ministry of the Interior declined to comment.

A decade after Russian troops drove separatists out of Chechnya in the second of two wars, the North Caucasus is plagued with violence almost daily, involving rebels fighting for a separate Islamic state.

Russia's top Islamist rebel Doku Umarov said earlier this week he ordered the devastating airport attack -- the second on the capital in 10 months.

He has pledged to inflict blood and tears on the Russian heartland ahead of 2012 presidential elections.

Though Dagestan is now widely seen as the epicentre of the insurgency, impoverished Ingushetia -- a sliver of land neighbouring Chechnya -- is also beset by violence.

President Dmitry Medvedev has told security officials that terrorism is Russia's biggest threat.