A rebel attack on Ukrainian troops has killed 30 and has caused an uproar within Kiev's government. However, the government is preparing to push the rebels out of cities and towns in the eastern part of the country.

On Friday, rebels fired missiles at a Ukrainian forward base near the Russian border, according to The Associated Press. The Ukrainian Interior Ministry confirmed the attack. An adviser to the ministry, Zoryan Shkiryak, pledged that those culpable would be brought to justice.

"They will be destroyed or captured and be made answerable to Ukrainian law," Shkiryak said.

A spokesman for the Interior Ministry confirmed that heavy casualties were incurred but did not give a specific number. However, border crossings and bases are important to both sides. They act as markers of Ukraine's territoriality, and the rebels can use them to rearm and attack from Russia, though Russia denies these allegations.

Russia's refusal to openly help the rebels helped in the recapture of Slovyansk by Ukrainian troops last week, and now Kiev is preparing to push forward but at great cost to civilians. According to the Wall Street Journal, the combination of Ukrainian tactics and rebels in urban areas has left many towns in shambles.

A battle near Slovyansk at a small town exemplifies what Ukrainians in conflict areas endure. Ukraine shells towns, and the projectiles do not accurately land on their desired targets, creating collateral damage. The Ukrainian army has said it will attempt not to hit civilian targets and many of the buildings in the town as in Slovyansk were not leveled but only some were hit.

As Ukraine moves its attention to Donetsk, however, there could be a danger of greater casualties. The city of 1 million is the next probable target for Ukraine, and the rebels have vowed to not let the city be retaken.

According to BBC News, rebels have retreated from various towns after the fall of Slovyansk and have regrouped within the capital of the rebel-controlled autonomous region of Donetsk. France and Germany continue to urge Russia to push the rebels into negotiations. However, Ukraine is preparing to attack the rebel-held city after a skirmish at the city's airport, the Chicago Tribune reported.

Igor Strelkov, the rebel commander, has said he will defend the city and suburbs, preventing it from being blockaded by Ukrainian troops, according to the BBC.

"We are counting on military support from the Luhansk republic in this respect, and we are confident that we have enough reserves to fulfill this task," he said. In the meantime, thousands continue to stream out of Donetsk ahead of an attack.