US President Barack Obama has left Warsaw, ending a four-country European tour that took him to Ireland, Britain, a G8 summit in France and lastly to Poland.
Air Force One departed the Polish capital after midnight AEST, an AFP journalist observed.
In Warsaw, Mr Obama met leaders from over a dozen ex-communist states looking at the lessons their own democratic and free market reforms could hold for the Arab Spring.
The US leader also raised joint US-Polish efforts for military and energy security in talks with Polish President Bronislaw Komorowski and Prime Minister Donald Tusk aimed at reaffirming bilateral ties with Poland.
Warsaw, which has emerged as a regional leader, assumes the rotating, six-month European Union presidency in July.
Mr Obama also paid homage to Holocaust victims at a monument dedicated to the wartime Warsaw Ghetto Uprising and met families of the victims of the April 2010 air crash in Russia in which Polish president Lech Kaczynski and 95 others, mostly senior Polish officials, perished.