An explosion in the town of Bucha, just outside Kyiv, injured two police officers after a second device detonated when officers arrived at the scene.
The blast happened in the early hours of Monday on a residential street.
Emergency teams rushed in after a loud initial explosion and were hit by a follow-up blast that wounded the two officers in their limbs; their injuries are not believed to be life-threatening.
Police have detained a 21-year-old local, saying he was recruited online to carry out two explosions.
Investigators are examining who else may have been involved.
A security source told the BBC the suspect was contacted through the online game World of Tanks.
Authorities say he was promised 25,000 hryvnyas (about £450 or $570) for each attack.
Footage released by police shows the suspect claiming he was coerced into planting the devices.
He alleges the people who contacted him threatened his mother, saying they could locate her by drone and would harm her if he refused.
The Ukrainian security service SBU described the arrested man as "a Russian agent," but police say they are still probing any direct links to Russia and have not confirmed that attribution.
Locals described a huge shock wave and at first feared a gas explosion.
The town council said eyewitnesses reported swift arrival of first responders and widespread alarm among residents.
Officials linked the incident to a series of recent attacks on law enforcement across Ukraine.
In late February, blasts in Lviv, Mykolaiv and Dnipro targeted police, leaving several officers dead or injured; Ukrainian investigators have said some past incidents involved operatives paid by Russian services.
