KIEV, Ukraine - Army troops have penetrated deep inside a rebel-controlled city in eastern Ukraine in what could prove a breakthrough development in the four-month-long conflict, the Ukrainian government said Sunday.

Germany says leaders may agree to continue Ukraine crisis talks

However, the military acknowledged that another one of its fighter planes was shot down by the separatists, who have been bullish about their ability to continue the battle.

Talks in Berlin between the foreign ministers of Russia, Ukraine, Germany and France aimed at finding a political solution to the conflict ended without any substantial result.

Ukraine's national security council said government forces captured a district police station in Luhansk on Saturday after bitter clashes in the Velika Vergunka neighborhood.

Weeks of fighting have taken their toll on Luhansk, which city authorities say has reached the verge of a humanitarian catastrophe. The siege mounted by government forces has ground delivery of basic provisions to a halt and cut off power and running water.