The U.S. government is urging Americans in to leave the country immediately, warning that is stepping up efforts to launch attacks on civilian infrastructure and government facilities ahead of Ukrainian independence day.
Wednesday's -- which commemorates 31 years since Ukraine broke its ties with the Soviet Union -- also marks six months since Russia's unprovoked invasion of the country.
"The U.S. Embassy urges U.S. citizens to depart Ukraine now using privately available ground transportation options if it is safe to do so," a security alert on the embassy's website said. "The security situation throughout Ukraine is highly volatile and conditions may deteriorate without warning."
The renewed U.S. alert comes follows similar warnings from and other officials that Moscow may carry out intense attacks, including missile strikes, around August 24.
"We must all be aware that this week Russia could try to do something particularly ugly, something particularly vicious," Zelensky said in a video message at the weekend.
Ukraine's government warned citizens to be "especially careful" on Tuesday and Wednesday.
"There is an increased threat of missile attacks and other provocations -- both inside the country and outside," said Andrii Yusov, a spokesperson for the Defence Intelligence service of Ukraine's Ministry of Defense.
"They are crazy about dates and symbols, so it would be quite logical to be on guard and be prepared for the fact that Independence Day will also be attacked. Ukraine is ready for this," he continued.
"The air raid alarm is a serious signal, that everyone should take into account. Especially on August 23 and 24 -- these are not just words, you have to be especially careful," Yusov added.
In Kyiv, the city military administration issued a ban on all big gatherings between Monday and Thursday, saying "it is forbidden to hold mass events, peaceful meetings, rallies and other events related to a large gathering of people."
Gen. Mykola Zhyrnov, head of Kyiv's military administration, said the order was imposed so that security forces could respond in a "timely manner to threats of missile and bomb attacks by the troops of the Russian Federation on decision-making centres, military facilities, defence industry facilities, critical infrastructure and nearby residential areas."
Last week, the State Department said it summoned Russian Ambassador to the U.S. Anatoly Antonov to a meeting so the United States "could warn Russia against any escalation of its war on Ukraine," a department spokesperson said Monday.
This included calling on Russia to "cease all military operations at or near Ukraine's nuclear facilities and to return full control of the Zaporizhzhya nuclear power plant to Ukraine," the official added.
The town of Nikopol across the river from the occupied plant suffered shelling on Ukraine's Day of the National Flag on Tuesday, a local official said.
Yevhen Yevtushenko, the head of Nikopol district military administration, warned locals to avoid mass gatherings, open areas and infrastructure facilities through Thursday.
Kyiv and Moscow have made a barrage of accusations against each other about security and military action at and around the plant, the largest nuclear complex in Europe. But the lack of independent access to the plant, which has been occupied by Russian forces since March, makes it impossible to verify what is happening there.
Recent satellite images from Maxar Technologies of the show no signs of "systemic shelling," despite claims by Russian President Vladimir Putin that the Ukrainian military was conducting repeated military strikes at the facility.
Tensions in the war spiked this week with, a Russian political commentator and the daughter of prominent ultranationalist ideologue Alexander Dugin.
Russia has blamed Ukrainian special services for her killing, according to Russian state news agency TASS.
"The murder of journalist Darya Dugina has been solved, it was prepared by the Ukrainian special services, by a citizen of Ukraine," TASS reported, citing Russia's Federal Security Service (FSB), which named a woman as the perpetrator and said she had fled to Estonia after the attack.
Ukraine has denied any involvement in Dugina's killing, calling the FSB claims fiction.
Dugina, the editor of a Russian disinformation website, died after a bomb planted in a car she was driving went off on the outskirts of Moscow on Saturday evening.
Dugina's father, , is a prominent Russian nationalist credited with being the architect or "spiritual guide" of Putin's invasion of Ukraine.
