The European Union has warned member nations Poland and Hungary that unilateral bans on Ukraine's exports of foodstuffs break the bloc's rules.

The EU's executive, the European Commission, issued the reminder after Poland and Hungary announced bans on Saturday that they said were necessary to protect their agricultural sectors from cheap imports of dairy products, fruit, grain, meat, sugar, and vegetables. The nations said the bans will remain in place until the end of June.

The EU, which is predominantly a trading bloc, said individual member nations are not free to adopt their own trading policies. The bloc did not say how it might try to persuade Poland and Hungary to rescind their bans.

"In such challenging times, it is crucial to coordinate and align all decisions within the EU," the BBC quoted an unnamed EU spokesperson as saying.

Poland and Hungary said the bans were needed because, ever since the start of the Russia-Ukraine conflict, foodstuffs that had previously been exported across the Black Sea have largely exited Ukraine via land borders. The change has led to a glut of Ukraine's exports in central Europe.

Waldemar Buda, Poland's economic development and technology minister, said his nation's ban will apply not only to items intended to be consumed within Poland but also to products destined for elsewhere.

"The ban is full, including the ban on transit through Poland," Buda wrote on Twitter.

Robert Telus, Poland's agriculture minister, said the ban should "open the eyes of the EU to the fact that further decisions are needed that will allow products from Ukraine to go deep into Europe, and not stay in Poland", suggesting an EU-led solution could be in reach.

Ukraine has criticized Poland and Hungary for banning its exports and said the prohibitions break bilateral trade agreements.

The BBC quoted Ukraine's agriculture ministry as saying it had "always been sympathetic to the situation in the Polish agricultural sector and responded promptly to various challenges".

"At present, unilateral drastic actions will not accelerate the positive resolution of the situation," the ministry said.

Ministers from Poland, Hungary, and Ukraine have scheduled talks to try to resolve the issue.

Reuters said the problem of relatively cheap Ukrainian food exports flooding markets in central Europe has been exacerbated by bottlenecks in supply chains that have prevented them from being shipped on.

Piotr Muller, a spokesman for Poland's government, told state-run news agency PAP that Warsaw is talking to the EU about the issue. He said the nation was entitled to break EU trade rules because of a clause that allows such action in cases of national security.

Bulgaria is also considering banning imports of Ukrainian foodstuff s, according to Bulgarian news agency BTA.