MOSCOW (AP) — Russian investigators say that Polish officials will be visiting Russia next month to re-examine the wreckage of a plane that crashed in western Russia in 2010, killing then-president Lech Kaczynski along with many other political and military leaders onboard.

Polish and Russian aviation experts have concluded that the 2010 plane crash was an accident, but Kaczynski's powerful twin brother alleges it resulted from foul play. Poland has set up an ad-hoc commission to re-investigate the crash.

Russia's Investigative Committee said in a statement on Thursday that it has agreed for Polish experts to visit the city of Smolensk in early September and attend an "additional" examination of the wreckage.

Moscow has not yet turned over the plane's wreckage or the flight recorders to Poland.