Russian President Vladimir Putin said Friday that Moscow would close established corridors for the export of Ukrainian grain if they were used to carry out “terrorist attacks,” CNN reported.

“If it turns out that these humanitarian corridors are being used for terrorist attacks, it will cast doubt on the grain agreement,” Putin told reporters in Kazakhstan’s capital, Astana.

On Friday, Putin suggested a link between the secure corridors and the recent attack on the Kerch bridge in Crimea, claiming that the explosives for the attack could have been sent by sea from Odesa.

Since July, ships carrying grain from the Ukrainian port of Odesa have been allowed to sail through a safe corridor across the Black Sea as part of a UN-brokered deal between Kyiv and Moscow after a five-month Russian blockade.

The deal is due to expire in November.

Putin’s remarks came as Russian diplomat Gennady Gatilov suggested on Thursday that his country could withdraw from the deal.

“If we see that nothing is happening on the Russian side of the agreement – the export of Russian grain and fertilizers – then, sorry, we will have to look at things differently,” he said, according to Reuters.

“We are not against grain supplies, but this agreement must be equitable, fair and properly implemented by all parties,” he added.