(CNN) -- Numerous world leaders were forced to cancel plans to travel to Poland for the funeral of President Lech Kaczynski on Sunday, as volcanic ash from Iceland continued to ground flights to and from Europe.
-- U.S. President Barack Obama
The White House said the United States would be represented at the funeral by Lee Feinstein, U.S. ambassador to Poland.
"I spoke with acting President (Bronislaw) Komorowski and told him that I regret that I will not be able to make it to Poland due to the volcanic ash that is disrupting air travel over Europe," Obama said in a statement.
"Michelle and I continue to have the Polish people in our thoughts and prayers, and will support them in any way I can as they recover from this terrible tragedy.
"President Kaczynski was a patriot and close friend and ally of the United States, as were those who died alongside him, and the American people will never forget the lives they led," Obama said.
-- French President Nicolas Sarkozy
Contrary to earlier reports that Sarkozy was already in Poland, his Web site said Saturday that "given the extreme weather that paralyzed the air traffic over most of Europe, (the) President of the Republic will not go to Krakow (Poland) to attend the funeral of President Kaczynski and his wife, as originally planned."
-- German Chancellor Angela Merkel
Germany will be represented by President Horst Koehler and Foreign Minister Guido Westerwelle.
Chancellor Merkel, returning from the United States, had her plane diverted to Lisbon, Portugal, and then to Rome, Italy, on Saturday. She then drove in a convoy up to the city of Bolzano in northwest Italy. She expects to drive back to Berlin, Germany, later Sunday.
Merkel called the Polish foreign minister Saturday night to express her apologies that she won't be able to attend, her spokesman said.
The foreign minister showed "great understanding," the spokesman said.
-- Prince Charles and British Foreign Secretary David Miliband
Miliband said both he and Prince Charles would be unable to travel to the funeral as scheduled.
"Because of the ongoing air travel disruption, it has become impossible for us to make the journey to the funeral, which we both deeply regret," Miliband said in a statement Saturday.
"We will be thinking tomorrow both of the families of all those who lost their lives in the plane crash and of the people of Poland."
Britain's Gordon Brown, who has been campaigning to hang on as prime minister since the parliament officially dissolved Monday, was never scheduled to attend.
-- Russian President Dmitry Medvedev
Medvedev left Moscow to attend the funeral, his office said early Sunday.
-- Other leaders who canceled
Canadian Prime Minister Stephen Harper, South Korean Prime Minister Chung Un-chan and Spanish Prime Minister Jose Luis Rodriguez Zapatero
-- Leaders who may attend
Estonian Prime Minister Andrus Ansip ditched plane tickets and opted to drive to Poland.
Latvian President Valdis Zatlers, a close friend of Kaczynski, also planned to make the 13-hour journey from his country to Poland by car.
Austrian President Heinz Fischer, Swedish King Carl XVI Gustaf and Bulgarian President Georgi said earlier they planed to attend if flights resumed in their countries.
European Commission President Jose Manuel Barroso was in Strasbourg, France, and was seeking alternative travel options to get to Poland.