Moscow (CNN) -- Two explosions damaged a phone booth and a building in eastern Ukraine early Thursday, and the apparent perpetrators promised more blasts if they do not receive a large sum of money, the Ukrainian Security Service said.
No one was injured in the explosions in the city of Makiivka, about 450 miles southeast of the capital, Kyiv, the security service said on its website.
At a news conference in Kyiv, Deputy Interior Minister Vasyl Farynnyk said an anonymous threat letter was left at the scene of one of the blasts, vowing five more explosions by the end of the day if the authors do not receive the money, according to Ukrainian media reports.
The first bomb exploded in a phone booth near a downtown shopping center, and the other one took place about 30 minutes later outside the office building of the state-owned coal enterprise, Ukraine's independent news agency UNIAN said.
Farynnyk said an envelope was glued to the wall of the office building, containing a demand for a large sum of money from "people who are well-known in Makiivka," as they called themselves, Ukrainian media reported. The letter, according to Farynnyk, contained instructions on how to conduct the money transfer.
The independent news agency Ukranews quoted other security officials as saying that the blackmailers were demanding that the government pay them 4 million euros.
Ukrainian President Viktor Yanukovych, who was on an official visit to Japan, decided to cut short his trip and return home, according to a statement on his official website.
When he gets back, he will meet with law enforcement and security chiefs, the statement said. In the meantime, he has instructed law enforcement agencies to tighten security in all regions of the country, the statement added.
The Ukrainian Interior Ministry reported on its website that an investigative task force has been established with several law enforcement agencies and counterterrorism units.
"The regional headquarters of the Anti-terrorist Center of the Security Service has consolidated all its efforts to identify the criminals and prevent new terror acts," said a statement on the Security Service website.
Additional police officers and demolition experts were dispatched to the area, according to local media.