Poland and Lithuania want to forge military cooperation with Ukraine to try to bring the former Soviet republic closer to Nato, Polish officials said.

Under the plan, the three countries would form a brigade that could participate in international peacekeeping operations under the auspices of the United Nations, the European Union or Nato.

"This reflects our support for Ukraine. We want to tie Ukraine closer to Western structures, including military ones," Poland's Deputy Defence Minister Stanislaw Komorowski told reporters in Brussels after signing a letter of intent.

"This is also proof that Ukraine is taking seriously its desire for closer cooperation with members of the EU and Nato," he said.

Eventual membership for Ukraine in Nato is a key issue in difficult relations between the Western military alliance and Russia after Nato's pledge to admit the former Soviet republic, as well as Georgia, greatly angered Moscow. The move by Poland and Lithuania, both of which are EU members, comes two days before an EU summit with Russia aimed at increasing cooperation with Moscow.

It also comes ahead of a visit in December to Moscow by Nato Secretary-General Anders Fogh Rasmussen, who has made boosting ties with Russia a top priority since taking over the Nato helm in August.

While the latest move could further anger Russia, a Nato spokesman welcomed the Polish-Lithuanian plan, saying cooperation could build up trust and capabilities.

"There is absolutely no reason why cooperation between individual allies and Ukraine should not be stepped up. If extra capability was made available for Nato operations that can only be welcome by the alliance," James Appathurai said.

Nato and Russia resumed formal cooperation on broad security threats after ties were frozen as a result of Russia's military intervention last August in Georgia, another former Soviet republic Russia sees as part of its sphere of influence.