(CNN) Russia will suspend its participation in the United Nations-brokered grain export deal with Ukraine after drone attacks on the Crimean city of Sevastopol, the country's defense ministry announced Saturday."Taking into account the act of terrorism committed by the Kyiv regime with the participation of British experts on October 29 this year against the ships of the Black Sea Fleet and civil vessels involved in the security of the 'grain corridor,' the Russian side suspends its participation in the implementation of the agreements on the export of agricultural products from the Ukrainian ports," the Russian defense ministry added in a statement.Russia pledged to unblock ports on the Black Sea to allow the safe passage of grain and oilseeds -- some of Ukraine's most important exports.Despite that, Ukraine's infrastructure minister voiced optimism about the deal earlier this month, saying "there is no doubt that the grain corridor will continue operating after Nov. 22," when it is set to expire.UN spokesman Stephane Dujarric told CNN Saturday: "We've seen the reports from the Russian Federation regarding the suspension of their participation in the Black Sea Grain Initiative following an attack on the Russian Black Sea Fleet."