Despite strong Ukrainian resistance, Russia remains determined to capture Kyiv, according to a Pentagon official.

• The pace of Russian advances towards Kyiv has slowed, with estimates from the Pentagon suggesting that Russian forces are approximately 25 kilometers (16 miles) away from Ukraine's capital.
• The U.K. Ministry of Defence's most recent public assessment stated that Ukraine retains control over Kharkiv and Chernihiv, both locations where intense fighting has occurred.
• A U.S. Defense official stated that the Ukrainians possess substantial air and missile defense capabilities.

Despite facing tough opposition from Ukrainian forces, the Kremlin remains determined to capture Kyiv with its invasion troops, according to a Pentagon assessment shared with CNBC.

According to a senior Defense official, who spoke on condition of anonymity to share new details from an assessment, there are indications that they still want to take Kyiv and are advancing on the ground to get closer.

The official warned that the distance of 25 kilometers (16 miles) between Russian forces and the Ukrainian capital is an estimate, and the movements on the ground are constantly changing.

The official stated that it is anticipated that they will continue to advance and attempt to surround Kyiv in the near future. However, this has not yet occurred, and it is unclear whether it will happen. Nonetheless, it seems that this is their objective.

The U.K. Ministry of Defence's most recent public assessment stated that Ukraine retains control over Kyiv, as well as Kharkiv and Chernihiv, which have been the sites of intense fighting for several days.

The Russian Armed Forces has for the first time acknowledged suffering casualties, despite efforts to conceal details of the conflict from the Russian population, according to the U.K. ministry.

Almost 200 tanks and almost 60 aircraft, half of them helicopters, have been lost by Russian invasion forces in Ukraine, according to the Ministry of Foreign Affairs on Monday.

CNBC is unable to independently confirm Ukraine’s claims.

Ukraine air power, communications

On day five, the Ukrainians have significant air and missile defense capabilities, as the U.S. Defense official revealed that the Russians began targeting Ukrainian missile defense capabilities early on.

Despite some intermittent outages, communications in Ukraine remain available, and the country's command and control remain intact, an official stated.

Ukraine's ability to coordinate its forces nationwide is primarily achieved through electronic means.

It is likely that Russian forces will continue to target Ukraine's air and missile capabilities, according to the official.

The US, EU, and individual EU states have pledged to send more weapons to Ukraine, including anti-aircraft and anti-tank missiles.

On Monday, the Wall Street Journal reported that EU member countries were discussing providing fighter jets to Ukraine, specifically Soviet-made planes, which Ukrainian pilots are familiar with.

Missile attacks, logistics problems

According to a U.S. Defense official, over 380 missiles have been launched by Russia. When asked about Russia's military capabilities, the official responded, "They're throwing a lot at the problem."

The official stated that they are deploying various types of missiles, including medium-range, short-range, and cruise missiles, as well as using artillery, rockets, manned aircraft, and infantry in the conflict.

Officials from both the United States and the United Kingdom maintain that Russian forces are facing difficulties with supply management and logistical issues.

Despite external reports suggesting Belarusian troops are operating in Ukraine, the U.S. official stated that the Pentagon has not seen any evidence to support this claim, as Belarus is closely aligned with Russia.

The official stated that based on our best information, all the forces within Ukraine are Russian.

According to a U.S. Defense official, nearly 75% of Russian forces positioned near Ukraine's borders have now invaded the country.