Russia warned that the security of ships sailing Ukraine’s grain-export corridor cannot be guaranteed without additional conditions, increasing risks for Black Sea trade after Russia halted involvement in a key accord. 

“The movement of ships along the security corridor is unacceptable,” Russia’s Defense Ministry said in a statement Monday, repeating unsubstantiated claims that Ukraine used the corridor for military purposes. The ministry emphasized that Russia hasn’t abandoned the deal but just suspended its involvement. 

The comments follow repeated criticism from Russian officials. Earlier, Ukraine said that Russia struck two civilian tugboats involved in transporting a grain barge near Ochakiv, to the east of the UN-agreed export corridor.

Grain prices surged after Russia said it was suspending its involvement in the deal. The UN said on Sunday that four vessels planned to move inbound and 12 outbound from Ukrainian ports on Monday. At least one of the inbound ships appeared to have turned back, while another did not enter the corridor. 

Turkish and Russian defense officials discussed the grains corridor by phone on Monday. The deal was brokered by Turkey and the UN.

United Nations Secretary-General Antonio Guterres is engaged in “intense” talks aimed at reversing Russia’s suspension, spokesman Stephane Dujarric said. The UN team at the Joint Coordination Centre in Istanbul will hold discussions with their Russian counterparts to “try to get some clarity” on the statement from Russia’s defense ministry, he said.