President Vladimir Putin is preparing to formally annex around 15% of Ukrainian territory after referendums on joining Russia in areas controlled by Russian forces or Russian-backed separatists.
Can the West stop Putin?
Neither the West nor Ukraine can stop Putin claiming the regions, though the United States and its allies say they want Ukraine to defeat Russia on the battlefield - and will help it do so by supplying weapons, but not NATO troops.
The United States is prepared to impose additional economic costs on Russia in conjunction with US allies if Moscow moves forward with annexing portions of Ukrainian territory, the White House said.
After imposing severe sanctions on Russia, though, there is not a great deal of economic punishment left to inflict unless the United States could get China and India to agree to some sort of cap on the price of Russian energy.
The West could send more advanced weapons to Ukraine.
Ukrainian President Volodymyr Zelenskiy said Ukraine had received sophisticated air defence systems, known as National Advanced Surface-to-Air Missile System (NASAMS), from the United States.
Zelenskiy has repeatedly warned that "pseudo-referendums" on annexation by Russia would destroy any chance of peace talks.
One of the senior figures in his administration, Mykhailo Podolyak, called on Tuesday for any referendums to be met by an increase in international economic sanctions on Russia and increased arms supplies to Ukraine, including Army Tactical Missile System, or ATACMS, a guided missile with a range of 300 km.
Which land will be annexed?
Russia plans to annex around 15% of Ukraine that its forces control as well as about 3% of Ukraine that it does not control - including frontlines where Ukrainian soldiers are still fighting, for example in the Donetsk region.
The areas include:
* A big chunk of eastern Ukraine, known as Donbas, where high concentrations of ethnic Russians and Russian-speaking Ukrainians live.
The two parts of the Donbas now include the self-styled Donetsk (DPR) and the Luhansk People's Republics (LPR), which Putin recognised as independent states just before the February 24 invasion. A frontline runs through Donetsk.
Referendums were held in 2014 in the two areas on secession from Ukraine.
* Russian-controlled Kherson region.
* Russian-controlled Zaporizhzhia.
Taken together, Russia would be annexing at least 90,000 square km of Ukrainian territory. That is an area around the same size as Hungary or Portugal.
Russia, which recognised Ukraine's post-Soviet borders in the 1994 Budapest Memorandum, annexed Crimea in 2014. With Crimea and the territory in the four other areas, Russia would have annexed at least one fifth of Ukrainian territory.
How quickly could formal annexation happen?
Fast. After the referendums, the Russian-backed leaders of the regions could ask to be included in Russia. Putin could swiftly approve and the legislation in Moscow would be passed fast.
After Russian forces on February 27, 2014 took control of Crimea, which has an ethnic Russian majority and was transferred to Ukraine in Soviet times, a referendum on joining Russia was held on March 16.
Crimea's leaders declared a 97% vote to secede from Ukraine and join Russia. Russia formally added Crimea on March 21, less than a month after invading it.
What does Putin say?
Putin says the Russians and the Russian-speakers of Ukraine have been persecuted by Kyiv and that he will never give them up to "executioners". Ukraine denies it has persecuted the Russian speakers, many of whom look to Moscow.
The Kremlin chief denies a distinct Ukrainian identity, saying it is an artificial construct partly the result of Bolshevik revolutionary Vladimir Lenin, who, after the Red Army took Kyiv, instituted the borders of the Ukrainian Soviet Socialist Republic after the collapse of the Russian empire.
In the 2001 Ukrainian census, 17% of people identified themselves as Russian with 78% of people identifying as Ukrainian. Ukrainian is by far the most spoken language in the country followed by Russian.
The conflict in eastern Ukraine began in 2014 after a pro-Russian president was toppled in Ukraine's Maidan Revolution and Russia annexed Crimea, with Russian-backed forces fighting Ukraine's armed forces.
About 14,000 people were killed in eastern Ukraine between 2014 and the end of 2021, according to the he UN Human Rights Office, including 3,106 civilians.