Update:

3:16 p.m.: In the wake of the latest escalations, the United Nations Security Council has scheduled an emergency meeting on Ukraine slated for this evening (at Russia's request) just hours before the premiere of Mad Men

Russia's Foreign Ministry said earlier it would put an urgent discussion of the situation in Ukraine on the Security Council agenda, calling Kiev's plans to mobilize the army to put down a rebellion by pro-Russian militants in eastern Ukraine "criminal"."

2:51 p.m.: Ukrainian officials have issued an ultimatum to the various groups of pro-Russian gunman and mobs currently holding court in government buildings across eastern Ukraine: Disarm by Monday or be disarmed.

Angered by the death of a state security officer and the wounding of two comrades near the flashpoint eastern city of Slaviansk, acting president Oleksander Turchinov gave rebels occupying state buildings until 0600 GMT to lay down their weapons."

This looming stand-off seems like the fulcrum point upon which this crisis could pivot into something else entirely.

12:42 p.m.: In the midst of all the turmoil, an anti-Kremlin rally took place in central Moscow today. Media freedom was the cause de jour and the demonstration was said to have drawn as many as 5,000 participants, some waving Ukrainian flags.

"Russia's main problem at the moment is lying, a problem leading to war in Ukraine, (and) the isolation of Russia from the rest of the world," said Igor Yakovenko, the former head of Russia's Union of Journalists, who helped to organize the protest."

12:38 p.m.: On "This Week," United States Ambassador to the United Nations Samantha Power promised more sanctions against Russia if it continues to foment unrest in eastern Ukraine.

The president has made clear that, depending on Russian behavior, sectoral sanctions in energy, banking, mining could be on the table, and there's a lot in between." 

10:54 a.m.: There are more reports that Kharkiv is the latest eastern Ukrainian city to have a government building attacked by pro-Russian forces. As many as 1,000 people stormed the city administration building this morning.

Earlier in the day, at least three people were severely beaten in Kharkiv around 3 p.m. on April 13 during clashes between Kharkiv supporters of the EuroMaidan Revolution and pro-Russian protesters, according to Glavnoe, a local news website. 

9:14 a.m.: According to reports, one Ukrainian soldier was killed and a number of others were wounded in a gun battle with a pro-Russian militia near the eastern Ukrainian city of Slovyansk earlier today. It was the first armed clash involving Ukrainian troops.

Vladimir Kolodchenko, a lawmaker from the area who witnessed the attack, said a car with four gunmen pulled up on the road in a wooden area outside Slovyansk and open fire on Ukrainian soldiers who were standing beside their vehicles. Both attackers and the Ukrainian servicemen left soon after the shooting."

The regional administration in Donetsk said that nine others were injured.

There were also accounts that contradicted an earlier report by Ukrainian Minister of Internal Affairs Arsen Avakov, who described a gun battle outside the Slovyansk police headquarters, which is currently held by pro-Russian gunmen. 

An Associated Press reporter saw no signs of any shots fired at the police station, which was surrounded by a reinforced line of barricades. Unlike on Saturday, the men patrolling the barricades were largely unarmed. One of the guards who asked not to be identified denied reports of fighting at the police station.

Original Post:

Ukrainian troops in the eastern city of Slovyansk were reportedly fired upon as they sought to take back a government building occupied by pro-Russian militants, according to the Ukrainian minister of the internal affairs. 

Arsen Avakov wrote on his official Facebook page that the pro-Russian "separatists" who seized the buildings in Slovyansk had opened fire Sunday morning on the approaching troops.

This appears to be the first serious military engagement between Ukrainian troops and pro-Russian forces—uniformed mobs, whose actions many believe are being directed by Moscow.

As we noted, Slovyansk was among the cities in the Donetsk region of eastern Ukraine to have its government buildings overrun by armed men yesterday. The buildings seized were the office of the Security Service and the police headquarters, the latter of which is the building that Ukrainian troops were aiming to retake when they were reportedly met by gunfire.