Ukraine's president recognised this was a "difficult" time for a summit
Ukraine's territorial integrity is "non-negotiable", France's Nicolas Sarkozy has affirmed at the end of an EU summit with the country in Paris.
Mr Sarkozy's reassurance comes after rising tensions between Russia and Ukraine over its Crimea region.
Ukraine has also been offered an association agreement with the EU, to be signed next year.
The accord represents cautious support for possible eventual EU membership for Ukraine.
"In the eyes of Europe, [territorial integrity] is absolutely non-negotiable," Mr Sarkozy said in a response to a question from reporters in Paris.
He underlined that the accord left the path for future membership of the 27-member state bloc open, saying: "This association accord does not close any avenues."
Ahead of the summit, Ukraine's president had sought a strong signal that the country belongs within Europe, diplomats said, to deter Moscow from intervening as it did in Georgia.
But the BBC's Emma-Jane Kirby, in Paris, said EU diplomats have been acutely aware of the risk of angering Russia by further strengthening ties between the former Soviet republic Ukraine and Europe.
"It is the maximum that we could do, and I believe that it is already an essential step," Mr Sarkozy said.
Mr Sarkozy emphasised that the accord was a recognised first step for countries with aspirations of EU membership.
Ukraine's President Viktor Yushchenko recognised the difficult timing of the summit and welcomed the association agreement as a successful outcome.
"We understand very well the conditions of this dialogue at present. This isn't the best time, given the situation in the region but we're patient," he said.
Fears have been raised that Ukraine, which has rocky relations with Russia, could find itself in a similar position to Georgia over South Ossetia.
Ukraine's Crimea region, like South Ossetia, is home to a significant Russian population. It also hosts a Russian naval base, which President Yushchenko has made clear he would rather not be there.
For the EU, Ukraine remains a key energy transit route and is seen as vital to the union's long-term security and energy strategy.
However some EU member states, including the Netherlands, Germany and Italy, have been reluctant to allow any explicit statement confirming Ukraine's future membership of the bloc.
The country is in the midst of political turmoil, following the collapse of its coalition government last week.
Mr Yushchenko threatened to dissolve parliament and call elections after his supporters walked out in protest at new laws to trim presidential powers.
The laws were introduced by the opposition and backed by his former ally Prime Minister Yulia Tymoshenko's bloc, now his rival in the upcoming presidential elections.