MOSCOW (AP) — 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.