Nearly four months after Russia invaded his country, Volodymyr Zelenskyy said there had been "few such fateful decisions for Ukraine" as the EU verdict expected this week.
"Only a positive decision is in the interests of the whole of Europe," he said in his evening address on Sunday.
"Obviously, we expect Russia to intensify hostile activity this week ... we are preparing. We are ready."
Moscow's forces are continuing to pummel eastern Ukraine in a bid to seize the Donbas region, after being repelled from other parts of the country.
Russian-backed separatist forces in Ukraine on Monday said they had taken a village beside the main southern road towards the eastern Ukrainian city of Severodonetsk, which has been the scene of fierce fighting for weeks.
Both sides have suffered significant losses in the battle for the city, which is in one of two self-proclaimed breakaway regions that Russia says it launched its invasion to defend.
Vitaly Kiselev, an assistant to the self-styled interior minister of the Russian-backed Luhansk People's Republic, was quoted by the Tass news agency as saying the village of Toshkivka, about 25 kilometres south of Severodonetsk, had been taken.
Serhiy Gaidai, the governor of the Ukrainian region of Luhansk, said pro-Russian forces were trying to break through the lines of the village.
The Ukrainian military said on Sunday that its forces had repelled heavy fighting near Toshkivka and other villages nearby.
Russia's Defence Ministry said Russian forces had taken Metyolkine, a district in the eastern suburbs of Severodonetsk. Mr Gaidai said Ukraine was no longer in control of Metyolkine.
Analysts at the Institute for the Study of War wrote in a note that "Russian forces will likely be able to seize Severodonetsk in the coming weeks, but at the cost of concentrating most of their available forces in this small area".
Since invading on February 24, Russia has scaled back its war ambitions, withdrawing troops from around the capital Kyiv and focusing on pushing Ukrainian troops out of the eastern Donbas region.
The UK's Ministry of Defence said the Russian air force has underperformed due to its failure to gain aerial superiority over Ukraine, contributing to Moscow's "very limited campaign success".
In an updated intelligence report, the MoD said Russia jets have been operating in a "risk-averse style" and have rarely penetrated front lines, putting pressure on its own ground forces.
"For years, much of Russia’s air combat training has highly likely been heavily scripted and designed to impress senior officials, rather than to develop dynamic initiative amongst air crews", the MoD said on Twitter.
Russian personnel have not developed the cultural skills needed to deliver a western-style modern air campaign, the MoD said.
The report said Russian ground troops were struggling with low morale and that supplies of cruise missiles were running low.
Nato Secretary General Jens Stoltenberg said the war could last for years and urged Western governments to continue sending state-of-the-art weaponry to Ukrainian troops, Germany's Bild am Sonntag newspaper reported.
"We must prepare for the fact that it could take years," Mr Stoltenberg was quoted as saying. "We must not let up in supporting Ukraine."
Ukraine's general staff said Russia had sent an anti-aircraft missile division to Bryansk and battalion tactical groups were covering the border in Bryansk and neighbouring Kursk regions.
Towards Kharkiv, the Russians were trying to stop Ukrainian forces from advancing to the border, it said.
In the south, western weaponry had helped Ukrainian forces advance 10km towards Russian-occupied Melitopol, its mayor said from outside the city in a video posted on Telegram.
Russia's Defence Ministry said it had launched missile strikes in the past 24 hours, with one attack on a top-level Ukrainian military meeting near the city of Dnipro killing "more than 50 generals and officers".
It said it had also struck a building storing western-provided weapons in Mykolaiv, destroying artillery and armoured vehicles.
There was no independent verification of these claims, however.