UPDATE 1-Respect constitution, EU's Tusk tells Polish leaders

European Council President Donald Tusk called on Poland's political leaders to respect the constitution during a speech in Warsaw on Friday, amid speculation that he may return to domestic politics when his EU term ends.

The former Polish prime minister and leader of the opposition Civic Platform party accused political leaders of celebrating the constitution once a year and disrespecting it on every other day, during his speech to mark the annual constitution day. "Poland is not the sick man of Europe," Tusk told a crowd of people at Warsaw University. "It can't be that those in power once a year celebrate constitution day, but disrespect it on a daily basis."

There is widespread speculation about Tusk's future once he leaves his European post, with Poland due to hold a parliamentary election in the autumn and a presidential election in mid-2020. Tusk did not announce a return to Polish politics on Friday.

He criticised political divisions in his home country, saying: "Today, specifically in our country, politics is taking on the character of a domestic war." Tusk's speech comes ahead of the European Parliament elections at the end of May in which more nationalist groups are expected to make gains.

The European Union has begun a legal procedure against Poland over changes to its judicial system by the governing nationalist party that EU officials say undermines democratic separation of powers and the rule of law. (Reporting by Joanna Plucinska and Jan Strupczewski Writing by Alicja Ptak; Editing by Janet Lawrence)