KYIV, Ukraine, Feb 16, 2024 (BSS/AFP) - Ukrainian President Volodymyr Zelensky on Friday instructed his government to "urgently negotiate" with Poland after Polish farmer protests brought more strain in relations between the allies.

Protesting Polish farmers caused uproar in Ukraine last week when they spilt Ukrainian grain on the ground during a protest on the border, in an incident Warsaw has apologised for.

Warsaw has been Kyiv's staunchest supporter against Russia but relations have taken a hit by several economic disputes in recent months.

"I instructed the prime minister of Ukraine to urgently negotiate with his Polish colleague (Donald Tusk)," Zelensky said in his daily evening address.

He criticised the grain pouring -- in which Polish farmers protested against what they see as unfair Ukrainian competition -- and called for improved ties.

"Ukrainian grain on the road is not just a few dramatic shots. This is evidence of how emotions can become dangerous," Zelensky said.

"We must, despite everything, protect good neighbourliness," he added.

The Ukrainian leader said Warsaw and Kyiv had a "common enemy in Moscow" and that they should "always negotiate with each other".

Poland took in more than a million Ukrainian refugees when Russia invaded in 2022, but some strains in relations developed in the second half of last year under a nationalist government in Warsaw.

Tusk, who travelled to meet Zelensky in Kyiv last month, has urged both sides to find a compromise.