WARSAW, Poland (AP) — A dispute about whether Ukrainian grain should be allowed to enter the domestic markets of Poland and other European Union countries has pushed the tight relationship between Kyiv and Warsaw to its lowest point since Russia invaded Ukraine last year.

Polish leaders have compared Ukraine to a drowning person hurting his helper and threatened to expand a ban on food products from the war-torn country. Meanwhile, Ukrainian President Volodymyr Zelenskyy suggested that EU allies that are prohibiting imports of his nation’s grain are helping Russia.

Poland, on NATO’s eastern flank, has been a staunch supporter of Ukraine, sending weapons and humanitarian aid and opening its borders to refugees.

Now, Polish officials, who are trying to win parliamentary elections next month with help from farmers’ votes, are expressing dismay over some of Ukraine’s latest moves, including a World Trade Organization complaint over bans on Ukrainian grain from Poland and two other EU countries.

“Alarmingly, some in Europe play out solidarity in a political theater — turning grain into a thriller. They may seem to play their own roles. In fact, they’re helping set the stage for a Moscow actor,” Zelenskyy said Tuesday during the U.N. General Assembly.

Poland’s deputy foreign minister, Pawel Jablonski, on Wednesday voiced “strong protest” of Zelenskyy’s comments to Ukrainian Ambassador Vasyl Zvarych.

Jablonski “indicated that it is untrue, as far as Poland is concerned, and that the opinion is unjustified toward the country that has been supporting Ukraine from the very first days of the war,” the Polish Foreign Ministry said in a statement.

Tadeusz Iwanski, a Ukraine analyst from a Polish state-funded think tank, said that since the beginning of the war, Ukraine “has been pursuing a hyperassertive diplomacy, partly due to which its requests and demands have been granted, and it has been proven effective.”

“This assertive policy might have taught Ukraine that things can be achieved through such diplomacy,” said Iwanski, head of Belarus, Ukraine and Moldova studies at the Centre for Eastern Studies in Warsaw.

He said Ukraine likely feels strong pressure to export its grain to help bolster its finances.

Meanwhile, Poland’s ruling Law and Justice party is fighting for the votes of farmers, many of whom are upset that Ukraine’s food products have flooded the local market, pushing prices down and hurting their livelihoods.

Poland, Hungary, Slovakia and Croatia banned some Ukrainian agricultural goods after the EU recently decided to lift such restrictions. Croatia joined in Tuesday, when Kyiv announced it was responding with a WTO complaint.

“Ukraine is behaving like a drowning person clinging to everything he can ... but we have the right to defend ourselves against harm being done to us,” Polish President Andrzej Duda told reporters Tuesday in New York, where he was attending the U.N. General Assembly.

The growing tensions highlight the risks Ukraine faces in maintaining Western support as its fight against Russia drags on.

Ukraine prevailing is so important to Poland that it would not be likely to restrict the military assistance to Ukraine. Poland has bitter memories of being subjected to Moscow’s rule in the past and does not want to see Russia win a war in a neighboring country.

Poland’s ruling party faces an election challenge from a new far-right coalition, Confederation, whose leaders complain that the country is doing too much to help Ukraine and claim Ukraine isn’t grateful enough.

The rift also shows how Ukraine and its neighbors are competing agricultural powers and how European defense of domestic farmers could complicate Kyiv’s hopes for a future path into the EU.

Ukraine — a major global supplier of wheat, barley, corn and vegetable oil — has struggled since Russia’s invasion to get its food products to parts of the world struggling with hunger. All the EU countries will keep allowing Ukrainian products to move through their borders to world markets.

Russia dealt a huge blow by withdrawing in July from a wartime agreement that ensured safe passage for Ukrainian grain through the Black Sea. That has left more expensive routes through Europe as the main way for Ukraine to get its products to developing nations where food prices have risen since Russia’s war began.

However, the first ship loaded with grain left a Ukrainian port this week under a temporary Black Sea corridor.

Ukraine also threatened this week to ban some Polish food items, but appeared to back off that. Such a move would bring only more bans from Poland, Prime Minister Mateusz Morawiecki said.

“I am warning the Ukrainian authorities, because if they escalate the conflict in this way, we will add more products to the ban on imports into Poland,” Morawiecki said Wednesday on Polsat News.

He argued that Ukrainian officials do not seem to understand how Poland’s agricultural market has been destabilized by the war.

In Bulgaria, the pro-Russia Socialist party has submitted a proposal to parliament to ban foods from Ukraine. So far, the government is just halting the import of sunflower seeds until a quota is agreed with Kyiv.

Prime Minister Nikolai Denkov announced the measure late Tuesday after lengthy talks with farmers who launched a nationwide protest last week over parliament’s decision to lift a ban on Ukrainian imports, citing higher food prices.

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Veselin Toshkov contributed from Sofia, Bulgaria.