Russia summoned the European Union’s ambassador to Moscow on Tuesday amid a blockade that has halted the shipment of many basic goods to a Russian outpost on the Baltic Sea in the latest round of sanctions over Ukraine. On the ground in eastern Ukraine, Russian separatist proxies have said they are advancing on the main stronghold of the Kiev battlefield. A Ukrainian official described the calm in the fighting as “calm before the storm”. The latest diplomatic crisis concerns the Kaliningrad enclave, a port and surrounding countryside in the Baltic Sea that hosts nearly a million Russians, who are connected to the rest of Russia by rail through EU and NATO member Lithuania. In recent days, Lithuania has closed the route to basic goods, including building materials, metals and coal. Vilnius and Brussels say Lithuania is implementing new EU sanctions that took effect on Saturday. Moscow has called the move an illegal blockade and has threatened unspecified retaliation. The EU ambassador to Moscow appeared at the headquarters of the Russian Foreign Ministry on Tuesday, the Russian state news agency RIA reported. During the night, the governor of Kaliningrad told Russian television that EU Ambassador Marcus Enterrer would be summoned and “briefed on the appropriate conditions involved here.” Nikolai Patrushev, secretary of Russia’s powerful Security Council, has arrived in Kaliningrad for a council meeting, RIA reports. Moscow had summoned a Lithuanian diplomat on Monday, but the EU withdrew responsibility from the Lithuanians. Vilnius “did nothing but implement the guidelines provided by the (European) Commission,” said EU foreign policy chief Josep Borrell. Inside Ukraine, the battle for the east has escalated into a brutal war of attrition in recent weeks, with Russia concentrating its overwhelming firepower in a Ukrainian-controlled enclave of the Donbas region claimed by Moscow. separatists. Moscow has made slow progress there since April in a relentless battle that has cost thousands of soldiers on both sides, one of the bloodiest ground battles in Europe in generations. MURAT YUKSELIR / THE GLOBE AND MAIL, SOURCE: GRAPHIC NEWS Fighting has been raging in the Siverskyi Donets River, which flows through the area, with Russian forces mainly on the east bank and Ukrainian forces mainly on the west, although the Ukrainians are still fighting in the east bank town of Sievierodonetsk. In recent days, Russia has seized Toshkivka, a small town on the west bank further south, giving it a possible foothold to try to cut off the main Ukrainian bastion in Lysychansk. Rodion Mirosnik, ambassador to Russia of the self-proclaimed Luhansk People’s Republic, a pro-separatist separatist, said forces were “moving south from Lyskhansk” with gunfire erupting in several cities. “The coming hours will have to bring significant changes to the balance of power in the region,” he told the Telegram. The governor of Ukraine’s Luhansk region said Russian forces had gained some ground on Monday. It was relatively quiet during the night, but there were more attacks, said Serhiy Gaidai: “It is a calm before the storm.” Although the fighting has favored Russia in recent weeks over the huge advantage of firepower in artillery, some Western military analysts say Russia’s failure to make a major breakthrough so far means that time is now on the side of the Ukrainians. Moscow is running out of fresh troops, while Ukraine is receiving newer and better equipment from the West, retired US Lt. Gen. Mark Hertling, former commander of US ground forces in Europe, wrote on Twitter. “It’s a heavyweight boxing match. In 2 months of fighting, there has not been a knockout yet. “It will come as RU forces become more depleted,” Hertling wrote.