Updated

A gunman carrying explosives has taken between 10 and 20 people hostage on a bus in northwestern Ukraine, authorities said on Tuesday.

It's not immediately clear whether anyone has been injured. Ukrainian President Volodymyr Zelensky, who is personally monitoring the situation in the city of Lutsk, said that the gunman took control of the bus at 9:25 a.m. local time.

“Gunshots have been heard, the bus is damaged,” Zelenskiy said in a Facebook statement. He added that authorities are attempting to resolve the situation without casualties.

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This image taken from video shows streets closed off, with an armored security vehicle and police car present, after an armed man seized a bus and took some 20 people hostage in the city center of Lutsk, some 250 miles west of Kiev, Ukraine on Tuesday July 21, 2020. 

This image taken from video shows streets closed off, with an armored security vehicle and police car present, after an armed man seized a bus and took some 20 people hostage in the city center of Lutsk, some 250 miles west of Kiev, Ukraine on Tuesday July 21, 2020.  (AP)

“We are in full control of the situation. I know all the details,” Zelensky said in a later statement from his press service, according to Reuters. “I am talking with our specialists who are in Lutsk. Professionals are working, doing everything to free our hostages.”

Police identified the gunman as 44-year-old Maksym Kryvosh, a native from Russia, Reuters reported. They found social media posts purportedly written by Kryvosh demanding that senior Ukrainian officials publish statements saying that they were terrorists. He also threatened to detonate another bomb in a crowded area.

Kryvosh had been convicted twice before and served about 10 years in prison, deputy interior minister Anton Gerashchenko said.

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Ukrainian law enforcement officers lie on the ground behind a car near a passenger bus, which was seized by an unidentified person in the city of Lutsk, Ukraine July 21, 2020. (Reuters/Tetiana Hrishyna)

Ukrainian law enforcement officers lie on the ground behind a car near a passenger bus, which was seized by an unidentified person in the city of Lutsk, Ukraine July 21, 2020. (Reuters/Tetiana Hrishyna) (Reuterd)

The suspect reportedly called the police himself after taking control of the bus and introduced himself as Maksim Plokhoy, Gerashchenko said on Facebook. The deputy interior minister said there is a book online titled "Philosophy of a criminal" which was authored by Maksim Plokhoy and describes a man's experience in prison. The word "plokhoy" translated from Russian means "bad."

“For 15 years they've been correcting me, but I haven't been corrected, on the contrary — I've become even more who I am,” one extract from the book said, according to Gerashchenko.

Police initially said in a video statement on Facebook that they also identified a Twitter account with that name, but did not find any specific demands, just messages displaying "general discontent about the system."

Authorities sealed off the center of Lutsk, which is located in the Volyn region about 250 miles west of Kiev, the country's capital. Interior Minister Arsen Avakov was also flying to the area.

Special Forces already made it to Lutsk and there are police officers at the scene "who are able to perform the task of neutralizing criminals," the head of police in the Volyn region, Yuriy Kroshko, said, according to Euro News.

Photos showed armored vehicles in the street. A blue-and-white passenger bus was seen with a broken window and most of its curtains drawn. Police officers were seen lying on the ground behind a car next to the bus.

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An eyewitness, Vitalik Troszyk, told Euronews he had heard "something like a gunshot" around 1:43 p.m. local time and that police was extending the security area, asking “people to keep their distance, go behind the houses." Troszyk posted a video to Facebook that showed a police roadblock on Voli Avenue in Lutsk.

The Associated Press contributed to this report