Poland's defense ministry says the country has reached a preliminary agreement with Bulgaria to modernize the Balkan country's Soviet-era fleet of MiG-29 fighter jets.

The deal comes as Bulgaria seeks to reduce its reliance on Russia in light of the Ukraine crisis, which has made many countries across the former Soviet bloc nervous.

The Polish Defense Ministry said a letter of intent was signed in Bulgaria on Friday between the defense ministers of the two countries, which are allies in NATO and the European Union.

Polish Defense Minister Tomasz Siemoniak said, "We are aware of the great importance of this decision and that it also has a geopolitical dimension."

Under the new deal, Poland would service, renovate and modernize Bulgaria's MiG-29s from mid-2016. The value of the deal wasn't disclosed.