Russian police check suspicious object in St. Petersburg

Young people hold candles as they gather to honor the memory of the victims of subway bombing on Marsovo Polye in St. Petersburg, Russia, Wednesday, April 5, 2017. A bomb blast tore through a subway train under Russia's second-largest city on Monday, killing several people and wounding more. (AP Photo/Yevgeny Kurskov) (The Associated Press)

People stand around candles showing the time of the subway bombing as they gather in memory of victims of the tragic event, on Marsovo Polye in St. Petersburg, Russia, Wednesday, April 5, 2017. A bomb blast tore through a subway train under Russia's second-largest city on Monday, killing several people and wounding more. (AP Photo/Dmitri Lovetsky) (The Associated Press)

People form digits of the time of the subway bombing in memory of victims of the tragic event, on Marsovo Polye in St.Petersburg, Russia, Wednesday, April 5, 2017. A bomb blast tore through a subway train under Russia's second-largest city on Monday, killing several people and wounding more. (AP Photo/Dmitri Lovetsky) (The Associated Press)

Russian law enforcement agencies are checking a suspicious object at an apartment building in St. Petersburg following a suicide bombing on the city's subway earlier in the week.

Russia's Federal Security Service (FSB) said, according to Russian news agencies, that the object found early Thursday in an apartment building on St. Petersburg's eastern outskirts could contain explosives. Residents have been evacuated and explosives experts have started working on the site.

Police in the city are on high alert following Monday's explosion that killed the attacker and 13 other people and wounded some 55.

Police on Wednesday arrested eight Central Asian migrants suspected of acting as recruiters for the Islamic State group and al-Qaida's Syria branch. The investigators found no immediate evidence of their involvement in the subway attack.