Updated

Russia's top domestic security agency says it has arrested seven suspected followers of the Islamic State group accused of planning a series of terror attacks in St. Petersburg.

The Federal Security Service, or FSB, said the suspects were plotting a suicide bombing and a series of other explosions in the city's busiest areas this coming weekend.

The agency said Friday that a search of a St. Petersburg apartment found explosives, automatic weapons and extremist literature. It said the suspects had received instructions from IS.

Earlier this week, the FSB said it arrested several IS-linked suspects in Moscow where they were plotting a series of suicide bombings during the New Year's holiday season.

In April, a suicide bombing in the St. Petersburg's subway left 16 dead and wounded more than 50.