Three Ukrainian nationals, including a Ukrainian oligarch, were injured after an explosive device detonated in a residential building, in what officials have described as Monaco’s first-ever terrorist attack.

Shortly before 9 p.m. local time, the wealthy, quiet city-state was rocked by the detonation of a bomb concealed in a backpack. Monaco’s Minister of State Christophe Mirmand said the bomb likely contained bolts and other material meant to turn it into an anti-personnel device. One of the wounded, and the likely target, was oligarch Vadim Ermolaev, one of Ukraine’s richest men. A woman in her 50s or 60s, described as Ermolaev’s “partner,” and a 13-year-old boy were also injured. The boy’s injuries were described as less severe, while Ermolaev and the woman are in critical condition.