NATO and the European Union's new president joined President Barack Obama in congratulating Viktor Yanukovich on Friday on his election in Ukraine.
NATO Secretary General Anders Fogh Rasmussen "warmly" welcomed Yanukovich's election -- although his presidential challenger Yulia Tymoshenko is yet to concede defeat.
"NATO is committed to deepening our strategic partnership with Ukraine, including by assisting, where possible, Ukraine's reform efforts, and I personally look forward to working closely with President Yanukovich," Rasmussen said in a statement, which emphasised that the election had been free, fair and democratic.
Herman Van Rompuy, the president of the EU council of ministers, who was appointed late last year to speak for the bloc's 27 member states, offered "whole-hearted" congratulations, stepping up the West's growing acknowledgement of Yanukovich.
"The European Union and Ukraine enjoy close relations based on common values and strong mutual interests," Van Rompuy said, referring to Yanukovich as "president-elect".
"In recent years the relationship between the European Union and Ukraine has deepened significantly... I trust that under your leadership our relationship will continue to thrive."
Russian President Dmitry Medvedev congratulated Yanukovich on his victory on Feb. 9, two days after the ballot.
Yanukovich, a 59-year-old ex-mechanic who wants to improve ties with Moscow but has also not turned his back on Europe, won the run-off vote by 3.48 percentage points, a margin of victory that Tymoshenko has refused to concede.
The team behind Tymoshenko, a co-architect of the pro-Western Orange Revolution of 2004, has accused Yanukovich's supporters of "cynical fraud" and is forcing a recount of votes in some regions.
Ukraine, squeezed between Russia and the European Union, is an essential transit route for Russian energy supplies to Europe. That has led it to be used as a proxy in the past, with Russia cutting off gas supplies to Ukraine for unpaid bills.
Western election monitors have widely described the vote as free and fair, adding to Yanukovich's legitimacy. As a result, Western leaders have slowly begun to welcome his victory.
The White House said on Thursday that the "peaceful expression of the political will of Ukrainian voters is another positive step in strengthening democracy in Ukraine".
Obama wished Yanukovich "success in carrying out his mandate" and "commended the Ukrainian people", a statement said.
French President Nicolas Sarkozy was the first EU leader to acknowledge Yanukovich's win, calling it a "victory for Ukrainian democracy". In a statement on Thursday he said the Ukrainian people have "expressed their choice in the course of free, pluralist and democratic elections."
The president of the European Parliament, Jerzy Buzek of Poland, also offered congratulations. Poland has historically been a strong backer of Ukrainian membership in NATO.