Shocking posters showed an ISIS fighter standing in front of the Kremlin with the caption "kill them where you find them".

The seat of the Russian government is collapsing in chilling images – which are reminiscent of those released by ISIS before the Westminster terror attack.

No one has yet claimed responsibility for the attack, but Russian authorities believe it was an act of terrorism.

ISIS supporters are reportedly celebrating the attack on St Petersburg which has killed at least 11 people and injured more than 40.

A briefcase bomb is believed to have detonated on the packed subway train in the bloody attack.

Another device was also found at a separate station in the city but it was dealt with before it could go off.

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Russian President Vladimir Putin, who is currently in St Petersburg on a visit, refused to rule-out terrorism.

Prime Minister Dmitry Medvedev has since described the incident as a terrorist attack.

(Image: AFP)

The attack came after 11 ISIS suspects were arrested in January for plotting attacks on Moscow and St Petersburg.

Video shows injured people lying bleeding on a platform, some being treated by emergency services. Others ran away from the platform amid clouds of smoke.

ISIS fanatics claimed responsibility for the terror attack at the Houses of Parliament weeks again – claiming it was the actions their "soldier" Khalid Masood.