* Putin's maritime ambitions include Black Sea, Arctic

* Russian missiles pound port of Mykolaiv

* Explosion in Russia's Black Sea fleet base

* Ukraine grain tycoon Oleksiy Vadatursky killed in Mykolaiv

* First Ukraine grain ship may leave port Monday

KYIV, Aug 1

Russian missiles pounded Ukraine's port city Mykolaiv on the Black Sea, as President Vladimir Putin signed a new naval doctrine casting the United States as Russia's main rival and setting global maritime ambitions in the Black Sea and Arctic.

Putin did not mention the conflict in Ukraine during a speech marking Russia's Navy Day on Sunday, but said the navy would receive hypersonic Zircon cruise missiles in coming months. The missiles can travel at nine times the speed of sound, outrunning air defences.

Navy Day celebrations in the port of Sevastopol were disrupted when five Russian navy staff members were injured by an explosion after a suspected drone flew into the courtyard of Russia's Black Sea fleet, the Crimean port city's governor, Mikhail Razvozhayev, told Russian media.

Reuters could not independently verify the battlefield reports.

Olga Kovitidi, a member of Russia's upper house of parliament, told Russia's RIA news agency that the attack was 'undoubtedly carried out not from outside, but from the territory of Sevastopol'.

'Urgent search operations are being conducted in the city to track down the organisers of this terrorist act,' Kovitidi was quoted as saying.

Mykolaiv Mayor Oleksandr Senkevych said more than 12 missile strikes on Sunday, probably the most powerful on the city in five months of war, hit homes and schools, with two people confirmed killed and three wounded. Missile strikes continued into Sunday evening.

Ukrainian grain tycoon Oleksiy Vadatursky, founder and owner of agriculture company Nibulon, and his wife were killed in their home, Mykolaiv Governor Vitaliy Kim said on Telegram.

Headquartered in Mykolaiv, a strategically important city that borders the mostly Russian-occupied Kherson region, Nibulon specialises in the production and export of wheat, barley and corn, and has its own fleet and shipyard.

GRAIN SHIPMENTS

Ukrainian President Volodymyr Zelenskiy described Vadatursky's death as 'a great loss for all of Ukraine'.

Zelenskiy added that the businessman - one of Ukraine's richest with Forbes estimating his 2021 net worth at $430 million - had been building a modern grain market with a network of transhipment terminals and elevators.

'It is these people, these companies, precisely the south of Ukraine, which has guaranteed the world's food security,' Zelenskiy said in his nightly address. 'This was always so. And it will be so once again.'

Putin invaded Ukraine on Feb. 24, setting off a conflict that has killed thousands, uprooted millions and deeply strained relations between Russia and the West.

The biggest conflict in Europe since World War Two has also stoked an energy and food crisis that is shaking the global economy. Both Ukraine and Russia are major suppliers of grain.

Zelenskiy said Ukraine may harvest only half its usual amount this year due to disruption to farming.

But an agreement signed under the stewardship of the United Nations and Turkey on July 22 provides for safe passage for ships carrying grain out of three southern Ukrainian ports.

The ship may leave Ukraine's ports on Monday, a spokesperson for Turkish President Tayyip Erdogan said.

EASTERN DANGER

Zelenskiy said Russia has been transferring some forces from the eastern Donbas region to the southern Kherson and Zaporizhizhya regions.

'But that won't help them there. None of the Russian strikes will go unanswered by our military and intelligence officers,' he said.

After failing to quickly capture the capital, Kyiv, early in the war, Russia has turned its forces on Ukraine's east and south.

Russia annexed Crimea in 2014 and Kyiv says Moscow is seeking to do the same with the Donbas region and link it to Crimea in the south. Russian-backed separatist controlled parts of the region before the invasion.

Russia said it had invited U.N. and Red Cross experts to investigate the deaths of dozens of Ukrainian prisoners held by Moscow-backed separatists.

Ukraine and Russia have traded accusations over a missile strike or explosion early on Friday that appeared to have killed the Ukrainian prisoners of war in the front-line town of Olenivka in eastern Donetsk.

The International Committee of the Red Cross condemned the attack and said it had not received permission to visit the site, while adding it was not its mandate to publicly investigate alleged war crimes.