Ukraine has relied on this innovative tactic to wreak havoc on Russia's Black Sea fleet, damaging or destroying a number of warships.

Russia prefers political and diplomatic means to resolve conflict in Ukraine, but Kyiv and the West rejected that path, Russian news agencies reported on Sunday, citing Kremlin spokesman Dmitry Peskov.

Russia on Sunday began direct commercial flights to North Korea, in a further sign of closer ties with its Asian ally helping its offensive in Ukraine.

The warring sides remain far apart after the third round of U.S.-brokered peace negotiations on Wednesday. But there was progress on humanitarian issues.

At the United Nations, Pakistan has expressed grave concern over devastating consequences of Russia-Ukraine conflict. Deputy Permanent Representative of Pakistan to the UN, Ambassador Usman Jadoon, at a briefing on Humanitarian situation in Ukraine, said Ukraine conflict is threatening peace and stability far beyond the region.

The Ukrainian president has rowed back from curbing anti-corruption bodies following a burst of public outrage. Some fear the damage has already been done.

Western defense companies are increasingly establishing new presences in Ukraine and working directly with Ukrainian companies.