Japanese Prime Minister Fumio Kishida pledged Wednesday to provide Poland with official development assistance to support the European country struggling to host refugees from neighboring Ukraine, which has been fighting to hold off Russia's invasion.

A day after his unannounced trip to Ukraine, Kishida met with his Polish counterpart Mateusz Morawiecki in Warsaw and, in a press conference afterward, welcomed Poland's role as "the frontline of military and humanitarian assistance to Ukraine."

The prolonged conflict has increased Poland's burden in accepting people fleeing from Ukraine in the wake of Russia's aggression since February last year.

Official data have shown that more than 1.5 million refugees are currently residing in Poland.

Japanese Prime Minister Fumio Kishida (L) and his Polish counterpart Mateusz Morawiecki hold a joint press conference in Warsaw on March 22, 2023. (Kyodo)

Kishida, who had entered Ukraine through Poland and revisited the country before returning home, stressed the importance of "like-minded countries' continued assistance" to end the war in Ukraine.

He and Morawiecki agreed to expand bilateral cooperation in security, economic and other fields, with the Polish leader saying "security cooperation with Japan will contribute to bolstering security in Europe."

Kishida's surprise trip to Kyiv, meanwhile, has come under fire by opposition lawmakers who pointed out that the government should have been more careful in preventing the leak of sensitive information about his itinerary.

Although details of his trip had not been disclosed due to security reasons, some media outlets ended up reporting about it.

In a parliamentary session in Tokyo on Wednesday, Chief Cabinet Secretary Hirokazu Matsuno explained that Kishida flew on a chartered plane to the southern Polish city of Rzeszow from India, which he had visited for talks with his counterpart Narendra Modi.

Kishida then moved from Poland to Kyiv by land aboard a train, Matsuno said, adding that the Ukrainian government was responsible for protecting him and that Japan's Self-Defense Forces were not involved.

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Japan PM vows continued support for Ukraine in unannounced visit