It was the family's first statement since the president and his wife, Maria Kaczynska, died in a plane crash Saturday in western Russia along with 94 others among Poland's political and military elite.
“It is the will of the family that, under no circumstance, the date of the funeral be changed,” Presidential Palace spokesman Jacek Sasin said on the family's behalf.
Airports in Poland were shut down Friday, however, as a cloud of volcanic ash drifting from Iceland forced huge patches of European airspace to be closed. It was unclear if Poland's airports would reopen in time to receive world leaders arriving early Sunday to attend the state funeral.
“There are situations we don't have any influence on,” Polish government spokesman Pawel Gras told Polish broadcaster TVN24. “The delegations will make their own decisions whether to cancel their presence in Krakow or to make use of other means of transportation.” The office of Slovak President Ivan Gasparovic said he planned to travel to Krakow by car for Sunday's funeral.
A national memorial service will be held Saturday at 12 p.m. (1000 GMT) in Pilsudski Square in Warsaw, followed by a Mass at St. John's Cathedral at 6 p.m. (1600 GMT) for the first couple.
Word of one cancelation for Saturday's ceremony came late Friday. The Polish news agency PAP reported that Cardinal Angelo Sodano, dean of the College of Cardinals, could no longer fly from Rome to deliver a memorial Mass there.
PAP quoted unnamed church sources as saying they still hope Sodano will be able to make it Sunday for the presidential couple's funeral in Krakow, perhaps by flying part of the way and making the last part of the trip by car.
Sunday's state funeral in mostly Roman Catholic Poland will begin at 2 p.m. (1200 GMT) with a Mass at the 13th-century St. Mary's Basilica. The bodies of the first couple will then be carried in a funeral procession across the Old Town and to the historic Wawel Cathedral, where they will be interred.
Among world leaders planning to attend Sunday are President Barack Obama, Russian President Dmitry Medvedev and German Chancellor Angela Merkel.
Foreign Ministry spokesman Piotr Paszkowski said the ministry had received “no information from any delegations about any changes in arrival. We are proceeding with the current plan.” Late Thursday, the White House said Obama would leave for Poland late Saturday.
On Friday Merkel was flying home from the US when her plane was diverted to Portugal because many of Germany's airports were closed because of the volcanic ash.
A Krakow airport spokeswoman said that while the airport was closed indefinitely, it was still preparing to receive world leaders on Sunday.
“A two-day perspective ahead of the arrival of those planes is a relatively long time,” Justyna Zajaczkowska told The Associated Press. “All we can do is wait.” Poland is preparing a tradition-laden funeral for Kaczynski and his wife, who were among the 96 people killed when their plane went down in heavy fog after clipping a birch tree on approach to Smolensk, Russia. They had planned to attend a memorial for thousands of Polish army officers executed in 1940 by the forerunner of the Soviet secret police in the nearby Katyn forest.
Polish investigators on Friday began examining one of three black boxes from the crashed Tupolev 154 plane, after Russian officials said their study of the boxes suggested pilot error was to blame.
The investigation is moving fairly quickly, aviation experts said, but some Poles have complained about a lack of public information, including the transcript of conversation in the cockpit before the accident.
Officials said they planned to release details from the black boxes only after the weekend memorial ceremonies. The black boxes are being examined for more clues as to why the plane crashed. Investigators from both Russia and Poland have said human error was likely to blame. The Polish pilot had been warned of bad weather and advised to land elsewhere, which would have delayed the Katyn observances.
Russia's Interstate Aviation Committee said the preliminary investigation found that the plane hit some trees about 1,050 meters (yards) from the paved runway, according to Russian state news agency RIA-Novosti, “After 200 meters, the left wing of the plane struck a tree, as a consequence of which the plane sharply heeled and turned over to the left,” the report said. “The main mass of fragments of the airliner are about 300-350 meters from the runway and about 150 meters to the left of it.” Tatyana Anodina, head of the Interstate Aviation Committee, said on Russian Vesti 24 television that the plane was working properly when it crashed.
“The data from both cockpit conversation and flight parameters recorders and analysis of fragments recovered from the crash site have shown that the plane's engines were functioning until it hit the ground,” she said.
“There was no fire or explosion on board.” Jerzy Artymiak, spokesman for Polish military prosecutors, said two black boxes are still being examined in Russia.
Late Friday, the remains of eight more bodies returned to Poland and were given a state ceremony at Warsaw's airport, their coffins laid out on the tarmac as a military band played Chopin's funeral march. Among them were Gen.
Franciszek Gagor, the Army chief of staff, and Wojciech Seweryn, a Chicago artist whose father died at Katyn 70 years ago.
“This is the sixth day that Poland welcomes its heroes back at this place,” Prime Minister Donald Tusk told relatives and soldiers gathered around eight coffins covered in the national flag and flowers.
