Ukraine officially joined the World Trade Organization on Friday, in line with an accession document signed by President Viktor Yushchenko and WTO chief Pascal Lamy on February 5.
"Ukraine has informed the WTO secretariat of joining the working group. In addition, the Ukrainian side has announced its intention to start tariff talks," the source said.
A new round of bilateral and multilateral talks on Russia's bid to join the WTO began in Geneva on Monday.
Despite earlier pledges by Kiev to help ease Russia's WTO membership, experts expected Ukraine to join the working group and request bilateral talks with Moscow in the energy and trade sectors.
Bilateral talks with Ukraine could delay Russia's accession to the WTO, so far planned for 2008.
Russia has been seeking membership of the global trade body since 1993. So far, Moscow has concluded bilateral talks with over 60 states, but still needs to complete discussions with two WTO members - Saudi Arabia and Georgia.
Georgian Reintegration Minister Temur Yakobashvili said last Friday that the country would continue to block Russia's entry to the organization until it withdraws its support for the breakaway Georgian regions of Abkhazia and South Ossetia.