What you need to know about the Ukraine-Russia crisis

Western leaders are warning that Russia has put in motion its plan to launch a full invasion of Ukraine, while announcing the first set of sanctions on Moscow.

President Joe Biden described events now underway in Ukraine as "the beginning of a Russian invasion," as he unveiled tough new measures to punish Moscow on Tuesday.

British Prime Minister Boris Johnson said Russia is "bent" on a "full scale invasion" of Ukraine, while German Chancellor Olaf Scholz said “Putin has built up enough troops along the Ukrainian borders to really be able to fully invade the country.”

Here's what you need to know.

What did Russia do? On Monday, Russian President Vladimir Putin ordered troops into Donetsk and Luhansk — two separatist-held pro-Moscow regions of eastern Ukraine — in what the Kremlin called a "peacekeeping" mission. The move came just hours after he signed decrees recognizing the independence of the regions.

Multiple US and Western officials cautioned this could serve as the opening salvo of a larger military operation targeting Ukraine. More than 150,000 Russian troops now encircle Ukraine on three sides, according to estimates from US and Ukrainian intelligence officials.

How has Ukraine responded? Ukraine’s response to a potential attack “will be instant,” Oleksiy Danilov, Secretary of Ukraine's National Security and Defense Council said Wednesday.

A State of Emergency is set to be introduced across all parts of Ukraine under government control, which will last for at least 30 days.

But the government has not closed the door to a possible solution. On Tuesday, Ukrainian President Volodymyr Zelensky said he is still pursuing diplomacy as a way out of the crisis; reservists would be called up for military training, he said, but there will be no general mobilization of armed forces.

"We desire peace and calm but if we are quiet today then tomorrow we will disappear," he said in an address to the nation.

How has the world reacted? Russia's actions have been strongly condemned by many nations, with Western leaders imposing new sanctions on Tuesday and cutting off a key pipeline with Russia.

Biden announced the United States will sanction Russia's financial institutions and oligarchs. The European Union also sanctioned 351 Russian lawmakers who voted to recognize the breakaway regions, and the United Kingdom announced sanctions against five Russian banks and three Russian oligarchs.

Also on Tuesday, Germany said it halted certifying an $11 billion 750-mile pipeline that connects Russia directly to Germany. The Nord Stream 2 project was completed in September but has not yet received the final green light from German regulators. Without that, natural gas cannot flow through the Baltic Sea pipeline from Russia to Germany.

On Wednesday, Japan and Australia joined the list of countries to impose sanctions on Russia, Donetsk and Luhansk.

But China, which for years has maintained a robust friendship with Russia, criticized Western sanctions. A Foreign Ministry spokesperson said Wednesday they are "never a fundamental and effective way to solve problems."