Ukrainian forces launched an operation against pro-Russian activists who seized a police station

 Ukrainian forces launched an operation against pro-Russian activists who seized a police station, the interior minister said on Sunday, in the latest of a series of protests that have rattled the east of the country.

Gunmen dressed in camouflage stormed and seized a police building in Slaviansk, a town about 100 miles from the Russian border on Saturday, and set up barricades around them.
In a post on his Facebook account, Interior Minister Arsen Avakov said an "anti-terrorist operation" had started in Slaviansk.
"It is managed by Anti-terrorist Center of the Security Service of Ukraine. All the law enforcement agencies of the country are participating. Godspeed!" Akakov wrote.
"Tell all civilians to leave the center of town - don't leave your apartment, or go to the window," he later added.
Kiev's fragile new government and the West accuse Russia of destabilizing the region as a pretext to potentially send in troops to protect the local Russian-speaking population.
NATO says Russian armed forces are massing on Ukraine's eastern border, while Moscow says they are carrying out military exercises.

Mounting strife
The gunmen in Slaviansk had arrived at the police station in two mini-buses. They opened fire at the police station before entering it through windows, Donetsk regional police said.
Three police officers were slightly injured.

The gunmen introduced themselves as part of the Donetsk republic initiative group. Their goal was to seize hundreds of weapons inside the police building; they allowed the police officers inside to leave the facility, the press office said.
A CNN team in Slaviansk saw dozens of armed, well-equipped men in camouflage in control of the Ukraine Security Services (SBU) building, as well as the police building. The men did not want to be filmed.
Makeshift barricades have been erected around both buildings and local residents brought food and tires to the armed men at the SBU site.

Tensions in Ukraine have become protracted. Violent street protests broke out months ago against the previous pro-Russia government and ended in the ouster of President Viktor Yanukovych.
Political power in the national government shifted rapidly in a pro-Western direction.
A short time later, pro-Russian elements occupied the region of Crimea, which Russia quickly annexed. Since then, pro-Russian protesters have taken to the streets in eastern Ukrainian regions, where Russian is widely spoken, and in some cases stormed and occupied buildings.
'People's republic'

The protesters' goal is to separate from Ukraine.
"We want to create a people's republic, a real one, one in Donetsk, one in Luhansk, and in general, let the people of the southeast determine what they want. We want to hold a referendum," one pro-Russian armed activist in Slaviansk told Reuters.
In Kramatorsk, also in the east, police and pro-Russia activists exchanged gunfire on Saturday, Avakov's spokeswoman Natalia Stativko said.
Acting Ukrainian President Oleksandr Turchinov held an emergency National Defense and Security Council meeting in the capital Kiev.
A police building in the town of Krasni Liman was also taken by protesters, Stativko said. The CNN team saw no evidence to that effect.
In the cities of Donetsk, Luhansk and Kharkiv, pro-Russian protesters seized government buildings several days ago and remain barricaded in some.

The Donetsk chief of regional police, Kostyantyn Pozhydaev, announced his resignation during a pro-Russia activist rally outside the police office Saturday, according to a police press statement.
The Head of the Security Service for the region, Valery Ivanov, was sacked, authorities said.
Washington, Moscow
The United States has accused Russia of fomenting the separatist unrest in its neighbor as a pretext for military intervention.

U.S. Secretary of State John Kerry spoke by phone with Russian Foreign Minister Sergey Lavrov Saturday, expressing "strong concern that attacks today by armed militants in eastern Ukraine were orchestrated and synchronized, similar to previous attacks in eastern Ukraine and Crimea," a senior State Department official said.
The official said that Kerry warned Lavrov there would be "additional consequences" if Russia did not take steps to de-escalate the situation in eastern Ukraine and move its troops back from its border.

The official also noted that militants involved in Saturday's unrest in eastern Ukraine "were equipped with specialized Russian weapons and the same uniforms as those worn by the Russian forces that invaded Crimea."
The White House also reacted Saturday, calling on Russian President Vladimir Putin and his government to "cease all efforts to destabilize Ukraine."
Vice President Joe Biden will travel to Kiev on April 22, to meet government leaders and members of the civil society.

Meanwhile, the U.S. Treasury on Friday imposed a third round of sanctions on individuals considered to be involved in Crimea's annexation, including six people the Treasury considers Crimean separatists.