Senior European Union officials who visited Ukraine have delivered a stern message to Kyiv that it has a lot more to do to secure membership, while they work on overcoming Hungary's opposition to Ukrainian accession.

Ukraine needs the backing of all 27 EU countries to become a member, but Budapest is blocking it from moving to the next stage of accession negotiations, citing concerns including the language rights of ethnic Hungarians.

Hungary's stance has frustrated other EU states, and the bloc's enlargement commissioner, Marta Kos, led a high-level charm offensive in Ukraine last week, meeting the Hungarian minority in the west of the country to try to ease tensions.