KYIV, Ukraine — Ukrainian forces Wednesday were putting up a fierce defense in Vovchansk, a village in northeastern Ukraine about 5 miles from the Russian border, engaging in what appeared to be street fighting as they tried to contain the Russian advance in the area.

In a sign of heightened concern over Ukraine’s deteriorating military situation, President Volodymyr Zelenskyy canceled his participation in all international events for the coming days, including a visit Friday to Spain where he was expected to sign a bilateral security agreement.

Ukraine’s General Staff said in a statement that its forces had “partially pushed the enemy” out of Vovchansk.

A few hours earlier, it had acknowledged that its troops had withdrawn from positions in two villages, including Vovchansk, allowing Russian forces to gain a foothold.

“Active fighting is ongoing,” Oleksiy Kharkivskiy, the police chief in Vovchansk, said Wednesday in a video published on Facebook from the village, in which heavy gunfire could be heard in the background.

He added that Russian troops had taken positions in several streets in the village and that the situation “is extremely difficult.”

Ukrainian officials and military analysts said Ukraine’s position on the battlefield in recent days has seriously worsened, as the government in Kyiv tries to repel a new Russian offensive push in the northeast that is stretching its already outnumbered and outgunned forces.

Russia has timed its new offensive, which started Friday, at an opportune moment.

Ukraine is short of manpower and is struggling to recruit more soldiers. It is also running out of ammunition because of delays in Western military aid, in particular the United States’ $60.8 billion package that was passed in Congress three weeks ago, after months of political wrangling.

Wrapping up a two-day visit to Kyiv, Secretary of State Antony Blinken said at a news conference Wednesday that the U.S. was “rushing ammunition, armored vehicles, missiles, air defenses” to the front lines.

Blinken added that the Biden administration had allocated $2 billion for Ukraine’s military, much of it to be invested in the country’s defense-industrial base to help Ukraine produce its own weapons over the long term.

Ukrainian officials and military analysts say Russia’s army now appears to be advancing more slowly in the northeast, six days into its offensive, partly because they have reached more urbanized areas, like Vovchansk, which makes rapid progress more difficult.

Gen. Kyrylo Budanov, head of Ukraine’s military intelligence agency, said on Ukrainian television Tuesday that conditions in the area under attack were moving “toward stabilization,” with additional Ukrainian units being rushed in to repel Russian advances.

But he added that “the situation is quite tense and is changing very quickly.”

The assessments by the Ukrainian officials and analysts appeared to be supported by open-source maps of the battlefield compiled by independent groups analyzing combat footage. Those maps showed that Russian troops had gained footholds in two settlements in the past day, a slower rate of advance than before, when they were capturing up to five settlements a day.

Russia’s Ministry of Defense said Wednesday that it had captured two settlements in the northeast, a claim that could not be independently confirmed and did not match what the open-source maps showed.

Russia also said it had seized the village of Robotyne in the south. The claim could also not be independently verified and Ukrainian officials denied it.

“They are only on the outskirts, our positions are still in the village,” Lt. Serhii Skibchyk, the spokesperson for the 65th Brigade, said in a comment to Ukrainian Pravda. “Both Ukrainian and Russian troops have fire advantage over the village simultaneously. But the majority of the village is still our position.”

Robotyne was recaptured by Ukrainian troops last summer, in one of the few gains of Ukraine’s unsuccessful counteroffensive at the time. Should it fall back into Russian hands, it could deal a blow to the morale of the Ukrainian army.

Vovchansk has been heavily bombed since the start of Russia’s offensive operations Friday, including with powerful guided weapons known as glide bombs that deliver hundreds of pounds of explosives in a single blast. Almost all the residents of the village, which had a prewar population of 17,000, have fled, local authorities said.

Oleh Syniehubov, head of the Kharkiv region’s military administration, said Wednesday that nearly 8,000 civilians had been evacuated from villages and settlements in the region. These include residents of villages on the immediate outskirts of Kharkiv that have come under increasing shelling in recent days.

Most evacuees have streamed into Kharkiv, hoping the city, Ukraine’s second largest after the capital, Kyiv, would provide them with more security. But Kharkiv has been the target of numerous Russian airstrikes for several weeks.

Syniehubov said Kharkiv had been targeted six times Tuesday, including with glide bombs that hit the northern part of the city, causing heavy damage to a 12-story apartment building and injuring 22 people.