But will they?
In a conversation urging a protest leader to accept the deal that was overheard by ITN/ITV, Sikorski pleaded, "If you don't support this, you'll have martial law, you'll have the army. You will all be dead."
The U.S. State Department official acknowledged the agreement is "a very tough sell" for many seething opposition activists, and called the deal "very, very fragile."
Speaking to CNN, Klitschko said he's listening to his side's dissenters and still pushing to maintain pressure on Yanukovych -- but not through violence.
"I tell everybody it is very important ... not to be involved in the war," said Klitschko, who called ensuring that the country doesn't "split" as a top priority. "(It's) also very important to find a peaceful way to be the winner."
Parliament acts to free opposition leader
Hours after that deal was signed, Ukraine's Parliament, the Rada, moved quickly to pass a series of measures seemingly in line with protesters' demands.
The first order of business was to fulfill the first requirement of the agreement -- passing a law to roll back the country's constitution to an earlier version that limits the President's powers.
Other bills called for the dismissal of the nation's interior minister and release of Yulia Tymoshenko, a former prime minister who earlier was a hero of the country's 2004 revolution, and who is a powerful symbol to the opposition.
A year after Tymoshenko lost the 2010 presidential election to Yanukovych and became his fiercest opponent, Ukrainian prosecutors charged her with signing overpriced gas deals with Russian state-owned energy provider Gazprom.
She was convicted and sentenced to seven years in prison at a trial she repeatedly called a farce overseen by a judge she called Yanukovych's "stooge." International observers criticized her trial as being a politically motivated sham.
Even with parliament's action, Tymoshenko's freedom was not expected to be immediate: A court must now act to free her, and other charges pending against her remain in place.
This wave of unrest began in November, amid anger about Yanukovych's decision to scrap a European Union-oriented trade deal and turn toward Russia.
Russia, which has offered to lend money to cash-strapped Ukraine in a deal worth billions of dollars and to lower its gas prices, has put pressure on Yanukovych to crack down on demonstrators.
Western leaders, who have offered Ukraine a more long-term aid package requiring economic modernization, urged the President to show restraint, open up the government to the opposition and let the democratic process work out.
Yet, fairly soon, it became clear that the discord wasn't just about Ukraine's ties to Europe or Russia, but about larger issues such as corruption and control. The opposition called Yanukovych heavy-handed, with Klitschko and others saying protesters wouldn't leave Maidan until the president resigns.
This tension boiled over Tuesday, when security forces waded into a Kiev crowd with water cannons, stun grenades, nightsticks and armored personnel carriers. At least 26 people -- protesters and police alike -- were killed.
Late Wednesday, the government announced it and opposition leaders agreed to a truce and to start talks aimed at a longer-term solution.
But it didn't last, collapsing in unprecedented gore in Kiev and unrest elsewhere in the Ukraine.