Here's a short primer on the events and the major players involved in the current confrontation.
Last November, Ukrainian President Viktor Yanukovych was expected to sign a landmark agreement with the European Union that would have resulted in a free trade deal between them, as well as closer political relations.
The association agreement, as the deal was officially called, would have pushed the former Soviet republic away from Russia, its No. 1 trading partner, and toward the West.
But Russia was troubled by the prospect of its loss of influence, and threatened trade sanctions against Ukraine. That's when Yanukovych walked away from the deal with the EU. His government said Europe did not offer compensation for the loss of trade with Russia.
Ukrainians who had wanted closer ties with Europe began protesting in Kiev's Independence Square. Police raided the event, and arrested more than 30 people, spurring even larger demonstrations that brought 100,000 people to Kiev.
There's been sporadic violence since the protests began, but none as serious as the clashes Tuesday. At least 25 people were killed and more than 200 wounded in the fighting between protesters and police, and both sides appeared to be digging in even deeper Wednesday.
As recently as this past weekend, there were signs of a compromise. Protesters agreed to vacate government buildings they'd occupied in exchange for the release of their detained comrades. It's unclear what sparked the violence. But The Associated Press notes:
"The latest bout of street violence began Tuesday when protesters attacked police lines and set fires outside Parliament, accusing Yanukovych of ignoring their demands to enact constitutional reforms that would limit the president's power — a key opposition demand. Parliament, dominated by his supporters, was stalling on taking up a constitutional reform to limit presidential powers.
"Police responded by attacking the protest camp. Armed with water cannons, stun grenades and rubber bullets, police dismantled some barricades and took part of the Maidan. But the protesters held their ground through the night, encircling the camp with new burning barricades of tires, furniture and debris."
Ukrainians themselves are deeply divided by the protests. Yanukovych draws his support from the Russian-speaking east and south of the country. But the biggest protests have been in the Ukrainian-speaking west of the country that borders EU nations. (The Washington Post has an excellent cartographical explanation of this division.)
Then there's the economy: Ukraine is struggling to recover from a recession, and the current unrest has resulted in capital flight, a currency in free fall and diminishing foreign exchange reserves. All of these factors are contributing to the political instability, which in turn is making the economy worse.
The Major Players
Yanukovych: To understand where the Ukrainian president stands and why there's so much animosity directed at him, we need to go back to 2004. That's when Yanukovych first won the presidential election. But his opponents said those elections were deeply flawed and held daily protests until he was ousted. Those events were dubbed the Orange Revolution.
But Ukraine's problems were not solved. Ukraine's new leaders, who were seen as Western-leaning, also became deeply unpopular, and when elections were held in 2010, Yanukovych won.
Protesters: We've told you about some of the more prominent opposition leaders, such as Vitali Klitschko, the former boxing champion. Then there's Arseniy Yatsenyuk, whom the U.S. apparently backs, according to a leaked phone conversation.
But the anti-government protesters are a disparate lot, ranging from democrats who want closer ties to the West, to civil society organizations as well as extreme right-wing groups. As the Economist noted, less than one-third belong to any organization.
Russia: The two countries share close historic and cultural ties, but there are also economic reasons behind Moscow's desire to retain influence over Kiev. Russia wanted Ukraine to join a Moscow-led customs union, together with some other former Soviet states.
Just how badly does Russia want to keep Ukraine in its sphere of influence? In 2008, when Kiev was considering joining NATO, President Vladimir Putin threatened to aim Russia's nuclear missiles at Ukraine. Two years later, Yanukovych said he was abandoning the country's bid to join the alliance.
Putin has steadfastly supported Yanukovych during the protests, and his Foreign Ministry called the violence a "connivance by Western politicians and European structures."
After Yanukovych walked away from the EU deal, Putin said Russia would buy $15 billion worth of Ukrainian bonds, giving the country a much-needed financial lifeline. Moscow made an initial bond purchase of $3 billion, put the payments on hold amid the violence, and then resumed them again this week.
West: The EU has threatened sanctions against the officials blamed for the violence and is holding an emergency meeting in Brussels on Thursday to discuss Ukraine.
"Possible sanctions include banning leading officials from traveling to EU nations or freezing their assets there," the AP reports. "Travel bans and assets freezes for the powerful oligarchs who back Yanukovych could prompt them to pressure him to change course."
The U.S., meanwhile, says its consulting with its partners on the situation in Ukraine.
It's unclear how much influence the West has in Ukraine. Western officials have met with Yanukovych as well as opposition leaders, but there have been no concrete steps laid out.