Russia continues to strike targets across Ukraine, causing damage and killing civilians, as its forces are preparing for battle in the strategic southern region of Kherson, Ukrainian officials and the military said.

Ukraine on October 26 reiterated its call for the development of an air-defense system to repel the Russian missile and drone attacks.

The immediate delivery of a sufficient number of air-defense systems is urgently needed to repel "Russian missile terror," the head of the president's office, Andriy Yermak, said after talks with the national-security advisers of the United States, Britain, and France in Kyiv on October 26.

On October 25, the head of U.S. aerospace and defense corporation Raytheon Technologies told CNBC television that Washington has already delivered to Ukraine the first two NASAMS medium-range antiaircraft missile systems.

“We delivered two systems to the U.S. government a few weeks ago. They are currently being deployed in Ukraine," Greg Geis said.

The General Staff of the Ukrainian armed forces said early on October 26 that more than 40 settlements were hit by Russian strikes during the previous day.

Russia used a combination of air strikes, rockets, and missiles to hit Ukrainian targets, the General Staff said in its morning report.

In the central city of Dnipro, at least two people, including a pregnant woman, were killed in the Russian bombardment, regional Governor Valentyn Reznichenlo said.

In the southern city of Kherson, Russian forces are digging in for the "heaviest of battles," said Oleksiy Arestovych, adviser to Ukrainian President Volodymyr Zelenskiy.

A Ukrainian counteroffensive has driven Russian forces back in the region, where the provincial capital of Kherson has been in Russian hands since the early days of the invasion eight months ago.

"With Kherson, everything is clear. The Russians are replenishing, strengthening their grouping there," Arestovych said in an online video late on October 25.

Russia-installed authorities are evacuating residents to the east bank of the Dnieper River as Russian forces prepare to defend the city, he said.

"It means that nobody is preparing to withdraw. On the contrary, the heaviest of battles is going to take place for Kherson," he said.

Zelenskiy on October 25 reiterated a pledge to retake the city of Kherson, the loss of which would be a big setback for Russian President Vladimir Putin.

Of the four Ukrainian provinces partially occupied by Russia that Putin proclaimed to have seized last month, Kherson is arguably the most strategically important.

It controls the only land route to the Crimea region that Russia illegally annexed in 2014 and the mouth of the Dnieper River that that bisects Ukraine.

Meanwhile, U.S. President Joe Biden warned Russia on October 25 that the use of a tactical nuclear weapon in Ukraine would be an "incredibly serious mistake."

Moscow over the weekend claimed Ukraine is preparing to use a so-called dirty bomb on its own territory, drawing immediate dismissal from the United States and other countries that have backed Ukraine.

Kyiv and its allies suspect Russia might have made the claim to set up a "false flag" attack in which it would use a dirty bomb itself but would blame the attack on Ukraine and use it to justify the use of conventional nuclear weapons by Moscow.

Russian Defense Minister Sergei Shoigu presented no evidence for the claim when he spoke on October 23 with his counterparts from several NATO countries, including Britain, France, and the United States, who dismissed the claim after the series of calls.

WATCH: Speaking to Current Time in Riga on October 22, Latvian Defense Minister Artis Pabriks said Russian President Vladimir Putin cannot change the course of war in Ukraine by dropping nuclear bombs.

Kremlin spokesman Dmitry Peskov told reporters on October 26 that Russia would "vigorously" continue to make the case to the international community that it believed Ukraine intended to detonate a dirty bomb with radioactive contaminants.

Peskov told reporters Moscow wanted to prompt an active response from the international community.

A dirty bomb would use a conventional warhead to create an explosion that would spread radioactive, biological, or chemical materials over an area.

Moscow took its accusations against Ukraine to the UN Security Council on October 25, and the country's UN ambassador, Dmitry Polyanskiy, said afterward that Russia was "satisfied because we raised the awareness."

Speaking to reporters, he added: "I don't mind people saying that Russia is crying wolf if this doesn't happen because this is a terrible, terrible disaster that threatens potentially the whole of the Earth."

The International Atomic Energy Agency (IAEA) said earlier on October 25 that it is preparing to send inspectors to two Ukrainian sites in the coming days in reaction to Ukraine's request for an inspection following Russia's claims.

Enerhoatom, Ukraine’s nuclear energy operator, issued a statement on October 24 voicing its concern that Russia’s statements “may indicate that Russia is preparing an act of nuclear terrorism.”

Russian troops have occupied Ukraine’s Zaporizhzhya nuclear power plant, Europe's largest, since March. It is still run by Ukrainian engineers though Russia claimed after its illegal annexation of the Zaporizhzhya region that it is on Russian territory.

Enerhoatom said that Russian forces have carried out unauthorized, secret construction work over the last week at the plant in the area of the spent nuclear fuel storage facility.

Russian officers controlling the area won’t give access to Ukrainian staff or monitors from the IAEA that would allow them to see what they are doing, the operator said.

Enerhoatom added that it “assumes” the Russians “are preparing a terrorist act using nuclear materials and radioactive waste stored” at the plant. (KB/RFE-RL)