A landmine in the al-Forosiyyeh district of Raqqa detonated overnight, the Syrian Observatory for Human Rights (SOHR) has reported.
It provided no details of human casualties, but said the explosion caused material damages in the former so-called capital of ISIS.
The city is under the security control of Raqqa Military Council that works in coordination with the Syrian Democratic Forces (SDF). It is predominately comprised of the mostly-Kurdish Peoples' Protection Units (YPG).
The SDF fought a four-month battle with massive coalition air support to liberate Raqqa from ISIS ending in October 2017.
Further south near the Euphrates River, the SDF detonated a vehicle-borne improvised explosive device in Baghouz.
The area in eastern Deir ez-Zor province near the Iraqi border is the last ISIS bastion.
"Heavy clashes are ongoing to pressure IS into surrendering," Rami Abdel Rahman, SOHR chief, told AFP.
ISIS is clinging to just a few square kilometers along the Euphrates River. Their military defeat is imminent, but the attack in Raqqa underscores that the group is capable of conducting asymmetrical attacks, thus reverting to an al-Qaeda like insurgency.
Many foreign fighters captured by the SDF have said that local Syrian Iraqi ISIS fighters have escaped and/or blended into the local communities.
A declaration of the military defeat of ISIS is imminent. US forces remain in Syria as part of the international anti-ISIS coalition, although the Department of Defense has acknowledged that equipment used by their units is being removed ahead of an expected full withdrawal of US forces within the coming months.
