UPDATE 5-Poland and Ukraine pledge quick end to political friction

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Poland pledges to help Ukraine beat Russia's invasion

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Zelenskiy says discussed bigger arms deals with Tusk

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Tusk's new government is preparing new package of aid

(Adds details, quotes from Shmyhal and Tusk)

By Dan Peleschuk and Yuliia Dysa

KYIV, Jan 22 (Reuters) - The leaders of Poland and Ukraine pledged on Monday to tackle political disputes that have hampered their critical wartime alliance and boost defence cooperation as Russia's invasion of Ukraine grinds towards its third year.

In his first visit to neighbouring Ukraine as prime minister, Poland's Donald Tusk delivered a message of friendship to President Volodymyr Zelenskiy and said both sides "have reached a common understanding" over protests by Polish farmers and truckers.

"Poland will do everything to increase Ukraine's chances of victory in this war," Tusk said at a joint media briefing.

Warsaw became a key ally for Kyiv as it sought Western financial and military support against Russia, but relations deteriorated in recent months when blockades at the border damaged Ukraine's economy.

The truckers agreed last week to suspend their protests, which had been aimed at revoking Ukrainian truckers' permit-free access to the European Union, until March 1.

Warsaw and Kyiv have also been at odds over Ukrainian grain exports to Poland and the rest of the European Union.

"We understand the depth of the reasons that led to this kind of situation, but draw attention first and foremost to the depth of the threat that stands before our peoples," Zelenskiy said, adding that he welcomed Warsaw's work on the issue.

Ukrainian Prime Minister Denys Shmyhal, in a separate briefing with Tusk, declared a "reset" in relations between the two governments and said they would hold regular meetings to strengthen cooperation.

He added that Kyiv would invest "maximum effort" to avoid harming Poland's economic interests, but that it also expected Warsaw to lift restrictions on Ukrainian farmers and producers.

"I am sure that we will find a solution that will benefit Polish farmers and producers and will be safe for the Ukrainian side," Tusk said.

"An honest conversation between friends can work wonders."

Zelenskiy and Tusk also hailed plans between their countries for joint arms production, and Zelenskiy said on X that they had discussed "a new form of cooperation aimed at larger-scale arms purchases for Ukrainian needs". He did not give details.

"We are going to invest in companies in Poland and Ukraine which will manufacture and function for the benefit of our defence capabilities in Poland, Ukraine, and the whole of Europe," Tusk said.

"This will be a very profitable business for both sides."

Poland's new government is also exploring how to make more ammunition and military equipment as part of a new aid package for Ukraine, Foreign Minister Radoslaw Sikorski said last week.

Shmyhal said Kyiv had received nearly $3.5 billion in military support from Poland since the beginning of the war.

Tusk's trip coincides with Ukraine's Unity Day, which celebrates the unification in 1919 of western and eastern Ukraine, which has faced numerous invasions over its long history.

Zelenskiy marked the day by announcing plans to offer dual Ukrainian citizenship to ethnic Ukrainians and their descendants from all around the world, apart from Russia. (Reporting by Yuliia Dysa, Dan Peleschuk, Paweł Florkiewicz and Felix Hoske; Editing by Bernadette Baum, David Goodman, Philippa Fletcher and Nick Macfie)