Ukrainian troops have taken possession of a police station within the city limits of Luhansk, which has been controlled by pro-Russian separatists for months, Reuters reported. Although Ukraine captured a key area of the city, its government said it has seen an increase in the number of trained fighters and military weapons coming from Russia.

Luhansk is vital because the separatists use the city to funnel aid from Russia into Ukraine, Reuters said. The capture of the police station marks the first time Ukrainian forces have been able to advance within the city limits, although the separatists have yet to give up control of the border area between Luhansk and Russia.

During the latest round of fighting, separatists shot down a Ukrainian fighter jet, with the pilot ejecting and being rescued by government elements. At the same time, separatist leader Alexander Zakharchenko said Saturday his forces were going to receive 1,200 troops and 150 armored vehicles, including 30 tanks, “at the most crucial moment.” Along a similar line, Reuters reported Ukrainian military representative Andriy Lysenko said three missile systems were seen crossing into Ukraine from Russia. Moscow has denied sending aid or helping the separatists during the four-month conflict.

A Russian aid convoy of close to 270 vehicles has been stopped at a town near the border of Ukraine and will need to be inspected before entering the country, the Associated Press reported. The humanitarian aid convoy was not authorized by the International Committee for the Red Cross, but the organization announced Sunday Russian and Ukraine officials will inspect the first group of trucks.

Foreign ministers from Russia, Ukraine, Germany and France were scheduled to meet Sunday to discuss the conflict, AP said.