Ukrainian President Viktor Yushchenko has backed his arch-rival Viktor Yanukovych for prime minister, ending a four-month political stand-off.
Mr Yushchenko (centre) wants his rival to back a pro-Western agenda
Mr Yushchenko said he acted after Mr Yanukovych had agreed to sign a pact that preserves key areas of the pro-Western president's policies.
He announced the move after a deadline for the PM's nomination passed.
It is a dramatic comeback for Mr Yanukovych, who was ousted in Mr Yushchenko's 2004 "Orange Revolution".
The president formally submitted the candidacy of Mr Yanukovych to parliament, which is expected to vote on the issue on Friday.
Some Orange Revolution supporters - including former Prime Minister Yulia Tymoshenko - see Mr Yushchenko's move as a betrayal, and they have accused the president of weakness, correspondents say.
Mr Yushchenko's aides say the president had little choice.
They say the other option - of dissolving parliament and calling new elections - would merely have sharpened the stand-off.
Ukraine has been in political turmoil since a parliamentary ballot in March in which no party won a majority, although Mr Yanukovych's Party of Regions polled the most votes.
Mr Yanukovych draws his support from the mainly Russian-speaking industrial southeast of Ukraine, where many voters are suspicious of the pro-Western, liberal Orange Revolution agenda.
"We have another chance to unite Ukraine today," Mr Yushchenko said in a televised address early on Thursday.
UKRAINE'S PACT - KEY POINTS
Ukraine to remain unitary state
Ukrainian is only state language
Goal of WTO membership by end of 2006
Goal of EU membership
Referendum on Nato membership
Constitutional reform - "checks and balances" system
It followed late-night talks as the two leaders negotiated the pact - a universal of national unity - which preserved policies championed by Mr Yushchenko.
"The pact... will determine the main lines of Ukraine's domestic and foreign policy, in which the Western course is guaranteed," he said.
The document was signed by the leaders of Ukraine's main parties later on Thursday, with the notable exception of Ms Tymoshenko.
Earlier in the day, Mr Yushchenko's Our Ukraine party and Mr Yanukovych's Party of Regions signed another deal - to form a coalition in parliament. They also urged other parties to join in.
The president had to decide by midnight Wednesday (2100 GMT Tuesday) whether to back the nomination of his rival for premier or dissolve parliament and call new elections.
Months of wrangling
"Whatever decision the president made, it would not have been accepted by part of the population," said Mr Yushchenko in his speech - several hours after the deadline passed.
21 Nov 04 Yanukovych declared winner of presidential election - protests begin
3 Dec 04 Election annulled
11 Jan 05 Yushchenko declared winner of re-run election
8 Sep 05 Yushchenko sacks Tymoshenko government
26 Mar 06 Yanukovych party wins most votes in general election
3 Aug 06 After four-month deadlock, Yushchenko agrees Yanukovych can be PM
Mr Yushchenko was brought to power by popular street protests in late 2004, which were sparked by outrage over Mr Yanukovych's presidential election win.
Mr Yanukovych - the then prime minister - was initially declared the victor, but the result was later annulled by the Supreme Court, which ruled that the vote was fraudulent.
Parliamentary elections on 26 March were followed by months of political wrangling.
The three parties which supported the Orange Revolution failed to form a government, and Mr Yanukovych created "an anti-crisis" coalition of parties which back closer ties with Russia.
The alliance then nominated him for prime minister, and Mr Yushchenko had to decide whether to forward the nomination to parliament.
The president has pushed for press freedom, tackling corruption, market reforms, Ukraine's membership in the EU and Nato.
He has also been urging for an immediate approval of all legislation required to join the World Trade Organisation.