Russia's drive to seize control of Ukraine quickly has lost momentum amid resistance from Ukrainian fighters on the ground and in the air, a senior US defense official said Friday.

"Their momentum, particularly as it comes to Kyiv, has slowed over the last 24 hours," the official said.

Russian forces, which entered Ukraine early Thursday, have yet to seize any major cities, or gain control of airspace, the official said.

"They have not achieved the progress that we believe they anticipated they would," the official said, speaking on condition of anonymity.

"A good indicator of that is no population centers have been taken. None," the official said.

The Pentagon believes that Moscow wants to seize control of Kyiv and replace the Western-leaning government with allies of the Kremlin.

And many worry that the powerful Russian force, with massive backup still awaiting on Ukraine's border, could conquer Kyiv within days.

But so far, while Russian forces have focused on military targets, they have not been able to disrupt the Ukrainian military structure.

"As we see it right now that Ukrainian command and control is intact," the official said.

Nor have they been able to command air space. The Pentagon says that Ukrainian air defense systems are still working and the country's air force is still able to fly and threaten Russian aircraft.

"They're meeting more resistance than they expected," the official said.

"We continue to have indications that it's not going quite the way that they had anticipated."

Starting with a massive missile barrage, Russia launched its invasion along three axes: the first a push from Belarus directly north toward Kyiv; the second from Russia's Belgorod region toward the major city of Kharkiv in northeast Ukraine; and the third, from Crimea in the south towards Kherson.

While Russian forces have reached the outskirts of Kyiv, they have not been able to enter, and fighting remains heavy around Kharkiv, which also has not fallen.

In the south, Russians continue to push to Kherson but are also widening the front, landing amphibious forces to Crimea's east to threaten Mariupol.

Russians have also sought to take control of the Kakhovka hydroelectric plant on the Dnieper river north of Crimea, launching cyberattacks on the plant, the official said.

The Pentagon would not estimate how many Russian forces had entered Ukraine, after having amassed more than 150,000 along the country's borders before attacking.

The official said that they had moved "about a third of their combat power" into Ukraine, and the rest remain in place just outside.

Zelensky asks Europeans with 'combat experience' to fight for Ukraine
Kyiv (AFP) Feb 25, 2022 –

Ukrainian President Volodymyr Zelensky on Friday called on Europeans with "combat experience" to take up arms and defend Ukraine against invading Russian forces, adding the West was too slow to help his country.

His dramatic call for help came as Russian forces were approaching the Ukrainian capital, with some units reportedly reaching the city's northern suburbs.

"If you have combat experience in Europe and do not want to look at the indecision of politicians, you can come to our country and join us in defending Europe, where it is very necessary now," Zelensky, who appeared tired, said in a video.

Speaking on the second day of the attack launched by Russian President Vladimir Putin, Zelensky also asked Europeans to "demand from your governments that Ukraine receive more financial, more military aid."

The 44-year-old leader also said the West was in no hurry to help Ukraine against the Russian invasion.

"How are you going to defend yourself when you are so slowly helping us in Ukraine?," he said.

"State institutions in Europe are not in a hurry with really strong decisions."

Western countries have imposed sanctions on Moscow, but stopped short of cutting Russia off from the SWIFT international payments system.

Zelensky demanded that Europe go further and "act without delay."

"Europe has enough strength to stop this aggression," he said.

"Cancellation of visas for Russians? Disconnect from SWIFT? Complete isolation of Russia? Recall of ambassadors? Oil embargo? Closing the sky? Today, all this must be on the table," he said.

The EU has said it could impose more sanctions on Russia in the future.

Ukraine said Russian forces were approaching Kyiv from the north and from the east on Friday.

Putin launched the attack on Ukraine in the early hours of Thursday.