An explosion that was apparently caused by a small bomb rocked an underground shopping mall adjacent to the Kremlin tonight, spraying glass shards and injuring 29 people, five of them seriously. Moscow Mayor Yuri Luzhkov called it an "act of terrorism," but the motivation behind the incident was unclear late tonight.

The blast occurred in a children's amusement arcade at Manezh Square, a collection of high-priced shops, fast-food outlets and other commercial enterprises just outside the Kremlin walls and near the parliament building. There are also several hotels in area, which is frequented by tourists.

Witnesses said that most of the injured--four of them children--were hit by flying plate glass from store fronts and video arcade machines. "There are a lot of shrapnel-type wounds," said Deputy Mayor Valery Shantsev. "The glass flew apart." The mall opened in 1997 but has had financial problems; from the outset there was an overabundance of retail space, while rents were among the highest in Europe.

Luzhkov said mall security personnel had received no threats or warnings. He said he did not think the blast was linked to any recent event, such as the conflict in Dagestan, where Russian troops are fighting Islamic rebels. He said the explosion was caused by a bomb containing about 5.3 ounces of TNT, whereas a spokesman for the Federal Security Service said the force of the explosion was equivalent to more than 10 ounces of TNT.

Police placed the Kremlin under tighter security after the blast.