Pro-Russian separatists occupying buildings in eastern Ukraine responded to a government ultimatum Wednesday by reinforcing barricades around areas they control with tires, barbed wire and car fenders.
The separatists stormed public buildings in the cities of Luhansk, Donetsk and Kharkiv on Sunday, demanding a referendum to join Russia like the one held in Crimea last month. U.S. officials contend the pro-Russian groups in eastern Ukraine are being backed by Russian agents and special forces.
The new Ukraine government, whose rule the protesters oppose, said earlier that the situation must be resolved diplomatically in 48 hours or they will resolve it with force.
"A resolution to this crisis will be found within the next 48 hours," Interior Minister Arsen Avakov told reporters in Kiev, Ukraine's capital.
In Luhansk, the separatists built new barricades using sandbags and wooden crates piled near the entrance of the state security building, and men with rifles could be seen through broken windows above, Reuters reported.
Just hours earlier, the security service said demonstrators had rigged the building with explosives and were holding some 60 hostages inside. The protesters denied they had used explosives or hostages, and dozens were later seen leaving the building.
Journalist Olaf Koens tweeted that he encountered a roadblock made of tires on the highway to the city of Donetsk, further south.
Inside the city itself, barbed wire barricades blocked some streets and protesters remained in control of the main regional authority building, according to a Reuters report.
Police ended the occupations in the city of Kharkiv, to the northwest, with an "anti-terrorism" raid on Monday night that saw some 70 people arrested.
Reuters contributed to this report.