By Tom Balmforth and Pavel Polityuk
KYIV (Reuters) -Fighting raged on Friday between Ukrainian and Russian forces near the town of Chasiv Yar, a Ukrainian stronghold in the east, but Kyiv denied that Moscow's troops had reached the suburbs.
Russian forces are inching forward in eastern Ukraine after capturing the bastion town of Avdiivka in February. Kyiv's soldiers are trying to dig in, facing long-term shortages of artillery shells with U.S. aid stuck in Congress.
Ukraine has needed the U.S. arms package for months in its fight with a much larger and better armed foe, and had hoped House of Representatives Speaker Mike Johnson would unveil an aid bill next week that would clear the Republican-controlled chamber.
But Republican infighting has created pressure to postpone it again.
A rapid Russian advance on Chasiv Yar, a heavily fortified town with a pre-war population of 12,200 situated west of the ruined, Russian-occupied city of Bakhmut, would be a grim setback for Kyiv.
Russia controls around 18% of Ukrainian territory and has stepped up its long-range strikes on energy infrastructure in recent weeks, causing large-scale outages.
Russia's RIA news agency cited an official as saying Russian troops had entered the suburbs of the town, which Moscow sees as an important staging point for Kyiv's troops.
Andriy Zadubinnyi, spokesman for Ukraine's eastern military command said the report was untrue and that fighting continued. He told Reuters the situation was "tense".
On Thursday, Serhiy Chaus, the mayor, said the situation in Chasiv Yar was at its most difficult since Russia began its full-scale invasion more than two years ago, in comments broadcast by the Espreso TV channel.
RUSSIAN WARPLANES DESTROYED, UKRAINE SAYS
Ukrainian President Volodymyr Zelenskiy said on Thursday that Ukraine had managed to stabilise its positions and that "given the shortage of shells and a significant slowdown in supplies, these results are really good".
Zelenskiy has said Russia may mount a new offensive in late May or summer, but that Kyiv has a battle plan of its own.
As Ukraine has gone onto the defensive, it has deployed hundreds of long-range drones to attack targets deep inside Russia.
A Kyiv intelligence source told Reuters that Ukraine's SBU security service and military had attacked an air base at Morozovsk in the adjoining Rostov region, destroying six Russian warplanes.
Reuters could not independently verify the claim. The source did not say how the attack was conducted but said eight more warplanes had also been damaged.
Russia's RIA news agency cited the Russian defence ministry earlier as saying air defences had downed 53 Ukrainian drones overnight, most of them over the Rostov region.
The source said the air base had been used by Russian tactical bombers that had fired guided bombs at Ukraine.