Russian forces enter the country's second largest city.. 3 prominent developments in the fourth day of the war in Ukraine and an American assessment of the weaknesses of both sides

Russian forces entered the second most important city in Ukraine, while some other fighting fronts witnessed a calm after the Russian Defense Ministry issued orders to all its forces to attack in all directions, while the deputy mayor of Kiev said that the capital witnessed several clashes with subversive groups during the night.

The capital, Kiev, witnessed the night of the firing of machine guns, while the sirens sounded in the city more than once, and some shells hit buildings in the city center near the government complex.

Russian forces enter the second most important city in the country

Regarding the course of the battles and efforts to control Kiev and the main cities in the country, Reuters quoted an adviser to the Ukrainian Interior Minister as saying that Russian forces entered the city of Kharkiv, which is the second largest city in Ukraine in terms of area and population, and is the ancient capital, and the largest industrial, cultural and scientific in the country.

The head of the State Administration Council in Kharkiv confirmed that the Russian forces entered the city and are being dealt with.

The Reuters news agency quoted the Russian Defense Ministry as saying that its forces are besieging the cities of Kherson and Berdyansk in southern Ukraine.

Regarding attempts to take control of the capital, the Ukrainian army confirmed that the Russian forces "continue their offensive to fortify Kiev" after they "completed the regrouping of their units" on the northern front.

Explosions at oil installations

In the most prominent developments for the fourth day of the Russian war on Ukraine, the mayor of Vasylkiv, southwest of the Ukrainian capital, Kiev, said in a video clip posted on the Internet that the town was hit by Russian missiles, which led to a fire in an oil facility.

The Ukrainian Defense Ministry stated that a Russian missile targeted the oil tanks at the Klu base, which is used to supply tanks with fuel and gas.

Ukraine's State Service for Special Communications and Information Protection also said on Sunday that Russian forces had blown up a natural gas pipeline in the Ukrainian city of Kharkiv.

It was not immediately clear how important the pipeline was and whether the blast could disrupt gas shipments outside the city or the country.

Despite the war, Ukraine continues to ship Russian natural gas to Europe.

Al-Jazeera correspondent in Kiev, Omar Al-Hajj, said that targeting fuel facilities represents a new chapter in the war that has been going on for days between Russia and Ukraine.

In another remarkable development, the Ukrainian Nuclear Energy Monitoring Authority said that a Russian bombardment hit a warehouse for storing nuclear waste in Kiev the moment workers were inside it.

The agency said that the workers at the facility had reported the injury to the place from their shelter, which they had taken shelter in during the bombing, by phone, and that they would not be able to reach it and determine the extent of the actual damage.

American evaluation

Two senior U.S. officials said Russian forces attacking Ukraine were facing "more severe than" resistance from the Ukrainian military

expected" as well as unexpected troop supply difficulties.

In statements to CNN, the two officials added that Russia was suffering "heavy losses" in personnel and aircraft more than expected, in part because Ukraine's air defenses were performing better than expected in US intelligence assessments before the Russian attack.

A senior US military official said Russia had not yet achieved an air advantage over Ukraine, as Ukraine's air defense systems and air forces are fighting for control of the airspace.

"Ukrainian air defenses, including aircraft, are still operational and continue to engage and block Russian aircraft," the official added.

An official said that as of Saturday evening, the United States had seen no indication that the Russian military had taken control of any Ukrainian city, even as Russian forces moved to cordon off some population centers, including the capital, Kiev.

One senior US official explained that Russia expected a quick victory and may have neglected to plan for adequate supplies, and one official explained that the supply lines were a "weakness".