Sergei Sobyanin said that Dmitry Pegov, previously the managing director of High-Speed Communications at the state-run Russian Railways company, has been appointed as the new Metro chief, Xinhua reported.
"What should be done first for now is to get to the bottom of the accident," Pegov told reporters Tuesday, adding that urgent measures should be taken to prevent such tragedies.
A Metro train derailed last Tuesday during an emergency braking in an underground tunnel in western Moscow, between Slavyanski Bulvar and Park Pobedy stations.
At least 23 people died and over 200 were injured in what is the worst accident in the Moscow Metro's history dating back to 1935.
Pegov pledged to restore faith in the Metro as the safest public transport service.
Two more suspects behind the accident were arrested Monday.
Russia's Investigative Committee (IC) spokesman Vladimir Markin said Alexei Trofimov, a senior executive in the Metro's repair department, and Anatoly Kruglov, chief operating officer of a subcontractor of the repair project, were detained for possible fatal negligence.
According to investigators, the accident was caused by a scattering of pointed blades left during repairs. Investigation is still continuing.
Moscow's health department said that 109 people injured in the accident are still receiving treatment in hospital as of Tuesday morning.
Investigators of the IC last Wednesday detained two persons suspected of violating transportation safety regulations -- the enterprise's track supervisor Valery Bashkatov and his assistant Yury Gordov.