The UK and European Union allies will support a new government in Ukraine "as and when that is formed", William Hague said as power appeared to have slipped from president Viktor Yanukovych.
The Foreign Secretary called for the country's political leaders to respond calmly as dramatic events unfolded in Kiev, including former prime minister Yulia Tymoshenko's return to the capital after two-and-a-half years in prison.
Ukrainian MPs voted to oust Mr Yanukovych - who left the capital for the security of his powerbase in the east of the country - and hold early presidential elections on May 25.
Mr Yanukovych described the events as a coup, insisted he was the "legitimately elected president" and said he would not step down.
Protesters, curious locals and journalists from around the world flocked to the vacated presidential compound to see for themselves Mr Yanukovych's opulent villa, complete with a collection of historic cars, a wooden galleon and a private zoo.
M r Hague said: "Events in the last 24 hours show the will of Ukrainians to move towards a different future, and ensure that the voices of those who have protested courageously over several months are heard."
He added: "We will work closely with our EU partners in support of a new government in Ukraine, as and when that is formed.
"In the meantime it is important that Ukraine's political leaders respond to events calmly and with determination to harness the united efforts of all Ukrainians to work together for a successful future."
Addressing the crown in Kiev's Independence Square, Ms Tymoshenko paid tribute to the protesters who had lost their lives in the unrest, saying "heroes don't die, they are always with us and they always will be our inspiration".
Speaking from a wheelchair amid occasionally chaotic scenes in the square, which has become the focal point for the opposition movement, Ms Tymoshenko said the protests should continue.
" Until you finish this job and until we travel all the way, nobody has the right to leave," she said. "Because nobody could do it - not other countries, nobody - could do what you have done. We've eliminated this cancer, this tumour."
Mr Hague and his German counterpart Frank-Walter Steinmeier held talks aimed at pushing for financial support for Ukraine.
A Foreign Office spokeswoman said: "One of the things they talked about was the economic situation and putting together a financial package which will help to stabilise the situation in Ukraine, to enable the Ukraine to receive long-term support from the IMF."
A US State Department spokesman said: " Going forward, we will work with our allies, with Russia, and with appropriate European and international organisations to support a strong, prosperous, unified, and democratic Ukraine."
With Mr Yanukovych refusing to accept the will of the country's MPs, fears mounted that the country could split in two - a Europe-leaning west and a Russian-leaning east and south.
"They are trying to scare me. I have no intention to leave the country. I am not going to resign, I'm the legitimately elected president," Mr Yanukovych said in a televised statement.
"Everything that is happening today is, to a greater degree, vandalism and banditry and a coup d'etat," he said. "I will do everything to protect my country from breakup, to stop bloodshed."