KYIV, Ukraine (AP) — Street fighting broke out in Ukraine’s second-largest city and Russian troops squeezed strategic ports in the country’s south Sunday, advances that appeared to mark a new phase of Russia’s invasion following a wave of attacks on airfields and fuel facilities elsewhere in the country. Following its gains on the ground, Russia sent a delegation to Belarus for peace talks with Ukraine, according to the Kremlin. Ukraine’s president suggested other locations, saying his country was unwilling to meet in Belarus because it served as a staging ground for the invasion. Until Sunday, Russia’s troops had remained on the outskirts of Kharkiv, a city of 1.4 million about 12 miles south of the border with Russia, while other forces rolled past to press the offensive deeper into Ukraine. Videos posted on Ukrainian media and social networks showed Russian vehicles moving across Kharkiv and Russian troops roaming the city in small groups. One showed Ukrainian troops firing at the Russians and damaged Russian light utility vehicles abandoned nearby. The images underscored the determined resistance Russian troops face while attempting to enter Ukraine’s bigger cities. Ukrainians have volunteered en masse to help defend the capital, Kyiv, and other cities, taking guns distributed by authorities and preparing firebombs to fight Russian forces.