Speculation and grief in Russia after terrorist attack

After one of the most serious terrorist attacks in Russian history, in which gunmen fired indiscriminately at concert-goers at a venue on the outskirts of Moscow, killing 133 people, many questions remain.

Another 152 people were injured, with many of them remaining in critical condition on Sunday, according to a report from the state news agency TASS, which cited the Moscow regional Civil Protection. Five children are reportedly among the injured.

Russia observed a national day of mourning on Sunday.

The Islamic State (IS) militia claimed responsibility for the deadly attack on the concert hall Friday night.

Eyewitnesses reported the perpetrators shot indiscriminately at visitors and that they heard explosions in the building before a major fire broke out.

Russian President Vladimir Putin hinted at a Ukrainian connection to the assault, without providing any evidence. Putin also claimed that the perpetrators of the attack attempted to flee in the direction of Ukraine.

Ukraine has adamantly denied any responsibility for the attack.

Intelligence services from the United States and other Western countries at the beginning of March warned of a potential imminent terror attack in Moscow. However, Putin dismissed the warnings as a Western provocation.

On Saturday, the so-called Islamic State's propaganda channel Amak published a picture of four people whose faces had been blurred.

Armed with assault rifles, pistols and bombs, the fighters had dealt Russia a "heavy blow," the statement said, adding that the attack targeted "thousands of Christians in a music hall."

During the night, heavy machinery cleared debris from the grounds of the Crocus City Hall.

According to the authorities, the clearing and recovery work should continue until at least Sunday evening.