What’s the latest?
Attacks to the north-west of Kyiv and an attempted incursion into the eastern city of Kharkiv were both repelled on Sunday, though in Ukraine’s southern coastal regions the Russian military appeared to be gaining strength.
In a sign that Russia was more actively targeting fixed infrastructure with missile attacks, an oil terminal was set ablaze in Vasylkiv, nearly 40km south-west of Kyiv.
Satellite images showed a large, 3.25-mile long deployment of forces in a convoy north-east of Ivankiv, moving in the direction of Kyiv approximately 40 miles to the south. The convoy contains fuel, logistics and armoured vehicles.
An incursion by Russian forces into the eastern city of Kharkiv was defeated, the Ukrainians said, a verdict largely confirmed by reporters on the ground.
In the latest signal from Vladimir Putin that he is prepared to resort to the most extreme level of brinkmanship is his effort to achieve victory, he ordered his military to put Russia’s nuclear deterrence forces on high alert.
What has happened since Russia invaded?
On Thursday Russia attacked Ukraine along multiple axes, bringing to a calamitous end weeks of fruitless diplomatic efforts by western leaders to avert war.
Fighting and other military activity took place around and on the way to Kyiv, including an ambitious attack by helicopters on the Hostomel military airbase.
Ukraine lost control of the Chernobyl nuclear site in the north, where fighting raged after Russian troops crossed the border from Belarus.
A substantial attack was also aimed towards the eastern city of Kharkiv.
Russian forces also headed north and east from Crimea. Social media footage showed them reaching Kherson on the Dnieper, 80 miles (130km) inside Ukraine.
On Friday Russian forces reached the outskirts of Kyiv, and carried out an amphibious assault from the Sea of Azov near Mariupol. The shape of the Russian incursion became clearer.
On Saturday Russian forces in control of territory to the north-west of Kyiv continued their assault on the capital. Moscow claimed its forces had taken control of the Hostomel airfield.
Elsewhere, heavy fighting was reported in and around Kharkiv and there were Ukrainian counterattacks in some places previously claimed by Russian forces, including Sumy in the east.
How did we get here?
Over the past few months Russia has forward-deployed hundreds of tanks, self-propelled artillery and even short-range ballistic missiles from as far away as Siberia to within striking range of Ukraine.
Moscow’s rhetoric also grew more belligerent. Vladimir Putin demanded legal guarantees that Ukraine would never join Nato or host its missile strike systems, concessions he was unlikely to receive. A flurry of diplomatic activity did little to ease tensions.
The second half of February was long seen as the most likely period for a potential offensive. Russian soldiers stayed on in Belarus beyond the end of planned military exercises, and the Winter Olympics, hosted by ally China, concluded.
The invasion was preceded on 22 February by Putin saying Russia would recognise the territorial claims of its two proxy states in east Ukraine. He had already ordered his forces into Russian-controlled territory in Ukraine.
On 22 February a Reuters witness saw columns of military vehicles including tanks and armoured personnel carriers on the outskirts of Donetsk, the capital of one of the territories claimed by Russia.
What do we know about Russia’s deployments?
Scores of battalion tactical groups – the smallest operational unit in Moscow’s army, consisting of about 800-1,000 troops – were put in place near the borders of Ukraine in both Russia and latterly Belarus prior to the invasion. As of 18 February the US estimated that Russia had between 169,000 and 190,000 personnel in and around Ukraine.
An estimated 32,000 separatist forces were already operating in the breakaway areas of Donetsk and Luhansk – some of whom were likely to be unacknowledged Russian forces – before the invasion.
Many of the heavy weapons stationed near Ukraine arrived as long ago as spring 2021. Over the new year Russia also began to move tanks, artillery, air defence systems and fighter jets to Belarus for joint exercises in February. That deployment has since grown.
Half of Russia’s air force is now deployed near Ukraine, according to western estimates. Russian warships conducted training exercises in the Black Sea in the run-up to the invasion. This footage released by the Russian defence ministry shows a Ka-27PS helicopter taking off and landing on the deck of a frigate during exercises on 22 February.
These satellite image composites show the buildup of troops in Yelnya and Pogonovo over the new year.
Satellite photographs also show increased deployments in Novoozernoye in western Crimea.
The US estimates that 10,000 troops moved into Crimea in late January and early February. This image from 18 February shows deployments including armour, helicopters and field hospitals in Novoozernoye:
Satellite images taken on 20 February showed troops and equipment being moved from holding areas to what the UK defence secretary described as potential launch locations.
How do the militaries compare?
Russia’s invasion pits the Kremlin’s large, recently modernised military against an adversary largely using older versions of the same or similar equipment, dating back to the Soviet era. Russia has significant numerical advantages on land and in particular in air and at sea, although the Ukrainians are defending their homeland.
What is the historical context?
In 2014 Putin sent troops to annex Crimea, a mainly Russian-speaking region of Ukraine. Russia also incited a separatist uprising in Ukraine’s south-east, clandestinely sending soldiers and weapons to provoke a conflict that grew into a full-blown war.
A 2015 peace deal established a line of demarcation and called on both sides to make concessions. Since then low-level fighting has continued along the front, and both sides have accused the other of violating the agreement.
Going back further, Russia has long opposed any attempts by Ukraine to move towards the EU and Nato. One of Putin’s often repeated demands is a guarantee that Ukraine never joins Nato, the alliance of 30 countries that has expanded eastwards since the end of the cold war.
What is the role of Nord Stream 2?
On 22 February, the German chancellor, Olaf Scholz, stopped the certification process for the Nord Stream 2 gas pipeline in response to Russia’s recognition of the two self-proclaimed republics.
First announced in 2015, the $11bn (£8.3bn) pipeline owned by Russia’s state-backed energy company Gazprom has been built to carry gas from western Siberia to Lubmin in Germany’s north-east, doubling the existing capacity of the Nord Stream 1 pipeline and keeping 26m German homes warm at an affordable price.
Europe’s most divisive energy project, Nord Stream 2 bypasses the traditional gas transit nation of Ukraine by running along the bed of the Baltic Sea. It has faced resistance within the EU, and from the US as well as Ukraine, on the grounds that it increases Europe’s energy dependence on Russia, denies Ukraine transit fees and makes it more vulnerable to Russian invasion.
