Catherine Ashton, the first senior foreign official to visit Kiev since Viktor Yanukovich was ousted as president, underlined the importance of Ukraine's territorial integrity in a signal to former Soviet master Moscow not to intervene unilaterally, Reuters reported.
"So we are here to say we want to support and help the country to stay strong and to go forward in the way it chooses to," Ashton told reporters after a second day of talks in the Ukrainian capital Kiev.
"We also think it is very important to send a strong message about the territorial integrity, and the unity and the independence of Ukraine."
Ukrainian parliamentarians have reported what they regard as "dangerous signs of separatism", a reference to concerns that Russian-speaking regions in the east and south might rebel or even try to break away with Russian support.
Ashton expressed hope that the new government being formed following Yanukovich's removal from power on Saturday would quickly come up with a plan to tackle the economic crisis.
She spelled out no details of any foreign financial assistance, but made clear the EU would work with the International Monetary Fund even though the IMF would make its own assessment of the situation.
"They will make their own decision, they have their own rules ... but are an important part of the jigsaw puzzle of trying to offer support," Ashton said.
She said a combination of short-term help and the role of long-term investment were needed.