MOSCOW, July 16./ITAR-TASS/ Work to restore train services on the Arbatsko-Pokrovskaya “blue” line of the Moscow subway, where traffic was partially disrupted on Tuesday when three train cars derailed killing over 20 people and leaving more than 200 injured, may be completed by the end of Thursday, Deputy Moscow Mayor Pyotr Biryukov said Wednesday.

“In line with the current schedule, movement of trains will resume on Friday morning, but there may be any unpredictable aspects in the situation that may both hold and speed up our work,” Biryukov told journalists.

“We are simultaneously studying what is on tracks, what is under broken cars, so it may be either way,” he said.

Biryukov said Moscow specialists and rescuers work side by side with investigators who keep working on the site. A total of 270 people are working on the site of yesterday’s tragic accident.

The tragic accident took place at 8:39 a.m. Moscow time (4:39 UTC) on Tuesday on the stretch of the west-bound "blue" line of the Russian capital’s metro network between the Park Podedy and Slavyansky Bulvar stations.

A rapidly moving train crashed entrapping all of its passengers in the underground tunnel after three of its cars derailed due to reasons that investigators have yet to establish.

Moscow Mayor Sergei Sobyanin declared Wednesday the day of mourning in the Russian capital.