Poland will expel four Russian diplomats as part of a wider European action to show unity with Britain over the poisoning of a former Russian spy in England that London has blamed on Moscow.

Tens of thousands of Poles dressed in black protested across the country on Friday against an attempt by the ruling conservatives and the powerful Catholic Church to ban most abortions.

Concessions in judicial reforms planned by Poland's ruling party are aimed at signalling to the European Commission that a compromise with Warsaw is possible, but will preserve the most important part of the reforms, the Polish prime minister said.

Poland's ruling party plans to change some of its judicial reforms in response to European Commission criticism that they threaten to undermine the rule of law, one of the party's lawmakers said on Thursday. Reacting to the lawmaker's comments, an EU official said there was a chance the two sides could reach a compromise.

Poland accused the European Union on Wednesday of "double standards" in its treatment of member states, a day after Brussels rejected Warsaw's defence of its court reforms that critics say threaten democracy.

The European Union executive on Tuesday dismissed Poland's latest defence of court reforms that critics say weaken democracy, potentially paving the way for more clashes with Warsaw after weeks of some rapprochement.

German Chancellor Angela Merkel will emphasise bilateral ties and the need for European unity when she meets with top Polish officials, amid ongoing differences between the allies over Polish judicial reforms, migration and a new gas pipeline.

Poland's Prime Minister Mateusz Morawiecki condemned on Wednesday an attempt to murder in Britain of former Russian double agent Sergei Skripal and demanded Russia, Poland's former master, to address the UK's questions regarding the case.

An Irish High Court judge has referred a Polish extradition case to Europe's top court over concerns that recent judicial reforms have been "so immense" that the rule of law in Poland has been systematically damaged.

If there is a hell, it was there. Maciej Starczewski tells the story of three prisoners of the extermination camp in Treblinka, the second largest in Europe. Over 800,000 people, mostly Jews from ghettos throughout occupied Poland, were gassed there over a period lasting just a year. The three witnesses featured in the program survived, because they escaped from the camp during a prisoner revolt in August 1943. It was one of the only two successful uprisings in death camps. They survived and gave their final testimony 15 years ago.

Polish climbers said on Monday heavy snow and ominous weather forecasts had forced them to call off their attempt to climb the world's second highest peak, K2, in winter - one of last remaining big feats in mountaineering.

Russian Defence Minister Sergei Shoigu said on Thursday that elements of NATO's anti-missile system deployed in Poland, Romania and Alaska were like an "umbrella with holes in it", Russian news agencies reported.

EU lawmakers on Thursday supported the European Commission's plans to take unprecedented punitive steps against Poland over reforms of its judiciary and state media that they say threaten the rule of law in the ex-communist country.

The European Union's top court on Thursday said Poland had failed to uphold air quality standards, part of a wider EU battle to reduce deaths from airborne pollution which it estimates kills 400,000 people every year.

Poland's decision to increase logging in a primeval forest breaks EU law, an adviser to the EU's top court said on Tuesday, backing the European Commission against the government in one of several disputes straining ties between Warsaw and Brussels.

Poland's government said Prime Minister Mateusz Morawiecki's comments saying Jews were perpetrators in World War Two as well as Poles and others, which were condemned by Israel, were not intended to deny the Holocaust.

The planned Nord Stream 2 gas pipeline connecting Germany and Russia poses no threat to Europe's energy security, Chancellor Angela Merkel said on Friday, publicly disagreeing with her Polish counterpart.

U.S. President Donald Trump plans to name Florida businesswoman and Republican fundraiser Georgette Mosbacher, whose husband served as U.S. Commerce Secretary under former President George H.W. Bush, as the U.S. ambassador to Poland, the White House said on Tuesday.

Ukrainian opposition leader Mikheil Saakashvili was deported to Poland on Monday, the Ukrainian border service said, after he was detained in a Kiev restaurant by law enforcement agents in camouflage. Poland's border service confirmed that he had arrived and that Warsaw had agreed to let him enter.

Polish authorities on Monday detained six people, including a former deputy treasury minister, on charges of negligence in their handling of the sale of a stake in chemical firm Ciech in 2014, a move the opposition said was politically motivated.