The malfunction caused one of the rocket's four side boosters to collide with the second stage of the rocket, Sergei Krikalyov said.
NASA astronaut Nick Hague and Russian cosmonaut Alexey Ovchinin safely aborted the mission-bound for the International Space Station-descending to Earth in a capsule and landing near the Kazakh city of Dzhezkazgan.
The Soyuz rocket launched at 08:40 local time (02:40 GMT) from the Baikanour cosmodrome site on 11 October when the malfunction occurred.
"The reason found by the commission (investigating the accident) was the abnormal operation of a sensor that signals the separation of the first and second stages", Krikalyov said at a space industry event in Moscow.
It was the third launch of a Soyuz rocket from Russia's northern Plesetsk launch pad this year, the military said.
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FILE - In this Thursday, Oct. 11, 2018 file photo, the Soyuz-FG rocket booster with Soyuz MS-10 space ship carrying a new crew to the International Space Station, ISS, flies in the sky at the Russian leased Baikonur cosmodrome, Kazakhstan. More recently, Russia's space program has been dogged by a string of failed satellite launches involving unmanned vehicles.
Russia, the only country able to ferry astronauts to the orbiting science lab, suspended all launches after a rocket failed on October 11 just minutes after blast-off -the first such incident in the history of post-Soviet space travel.
Roscosmos officials on Wednesday met with their counterparts from NASA to give them a full briefing of the incident, Roscosmos director general Dmitry Rogozin said on Thursday.
But the failure is worrisome, since Soyuz is the only human-rated spacecraft now used to get people to and from the International Space Station.
Space Daily carries an Agence France Presse report which said with the cause identified, Roscosmos believes it could conduct a crewed launch well ahead of the ISS's deadline.
Three crewmembers will launch toward the International Space Station (ISS) atop a Soyuz on December 3, Russian space officials announced today (Nov. 1). Russian Federation stands to lose that monopoly with the arrival of SpaceX's Dragon and Boeing's Starliner crew capsules.