At a NATO summit in Romania earlier today members voted to postpone offering the former Soviet republics of Ukraine and Georgia the chance to join the alliance's Membership Action Plan (MAP), and decided to reconsider their bid in December.
Protesters in Donetsk are waving "No to NATO" banners and further demonstrations are expected in the capital Kiev and across the country's southern and eastern regions.
A member of the opposition Party of Regions, Yelena Bondarenko, said the rally would last until the party, led by former prime minister Viktor Yanukovych, succeeds in "defending the freedom of Ukrainians on joining NATO or keeping the non-aligned status [for the country]."
Ukraine's drive toward NATO membership has triggered domestic parliamentary opposition protests amid widespread antipathy toward the alliance. And anti-NATO protesters have been gathering on Kiev's main square since Monday.
Ukrainian President Viktor Yushchenko reiterated earlier this week his promise to hold a referendum on the country's entry to NATO, a move demanded by the Ukrainian opposition, but pledged his support for membership in the alliance.
According to a survey published last month, only 11% of Ukrainians supported the idea of NATO membership, while almost 36% were strongly opposed.