Russia's Defense Ministry said on Tuesday it had hit military targets in two Ukrainian port cities overnight as "a mass revenge strike" following a "terrorist attack" on a key Crimea bridge.

The ministry said it had struck Odesa, where the Ukrainian navy has its headquarters, and Mykolaiv, near Ukraine's Black Sea coast.

"At night, the Armed Forces of the Russian Federation delivered a group retaliation strike with high-precision sea-based weapons at facilities where terrorist acts against Russia had been prepared using unmanned boats," it said in a statement.

On Monday, Russian President Vladimir Putin said in a televised meeting that the Defense Ministry was "preparing relevant proposals "and Russia will "of course" respond to the "terrorist attack" against Crimea's Kerch Bridge.

He called on the authorities, including the Federal Security Service, to investigate the incident and asked for measures to secure the "strategically important transport facility" from future strikes.

Putin also claimed there was no military significance to hitting the bridge because it "has long not been used for military transport". It is also a "brutal" crime since innocent civilians have been killed, he said.

The incident happened as Moscow announced the termination of the Black Sea grain deal. However, the Kremlin said the decision was unrelated to the bridge incident.

United Nations Secretary-General Antonio Guterres signaled that Russia's withdrawal meant the related pact to assist Russia's grain and fertilizer exports was also terminated.

Profound impact

Shashwat Saraf, emergency director in East Africa for the International Rescue Committee, said the impact would be profound in Somalia, Ethiopia and Kenya, which have been facing the Horn of Africa's worst drought in decades.

Kremlin spokesman Dmitry Peskov told a briefing on Tuesday that Moscow rejected a United States' criticism of its withdrawal from a grain deal backed by Turkiye and the UN. Russia would continue supplying grain to poor countries, he said.

He added that the grain deal zone "is used by the Kyiv regime for combat purposes".

Also on Tuesday, Russia's Defense Ministry said on Telegram that a total of 28 Ukrainian unmanned aerial vehicles targeting Crimea were intercepted by air defenses, but there were no casualties or damage from what it described as a "terrorist attack".

Russia has been accusing Ukrainian forces of striking its supply lines, while Kyiv said Russia had amassed "over 100,000 troops and more than 900 tanks" in northeastern Ukraine's Kupiansk city.

Agencies contributed to this story.