Sept. 6 (UPI) -- A Russian rocket strike on a public market in the eastern Ukrainian city of Kostiantynivka killed 16 people Wednesday, officials said.

"As of 16:00, 16 people were killed in the attack by occupiers. A further 31 people were injured, and they are receiving emergency medical care," the Ukrainian prosecutor general's office said.

People were trapped under the rubble.

"Russian terrorists have attacked a regular market, shops and a pharmacy, killing innocent people. The number of casualties could rise further," Ukrainian President Volodymyr Zelensky posted on X.

"Anyone in the world who is still dealing with anything Russian simply ignores this reality. Heinous evil. Brazen wickedness. Utter inhumanity. My condolences to everyone who lost a loved one. The Russian evil must be defeated as soon as possible," he said.

Security footage posted online shows a blast ripping through part of the market in the Donetsk region with civilians present.

Ukrainian officials said they have opened an investigation into the attack.

"Under the procedural leadership of the Donetsk regional prosecutor's office, a pretrial investigation was started in criminal proceedings for violation of the laws and customs of war," the prosecutor's office wrote on Telegram.

The attack comes as U.S. Secretary of State Antony Blinken arrived in Kyiv to discuss Ukraine's ongoing counteroffensive.

"We want to make sure that Ukraine has what it needs, not only to succeed in the counteroffensive, but has what it needs for the long term," Blinken said in a meeting with Ukrainian Foreign Minister Dmytro Kuleba.