Russian forces appeared to be moving to cut Ukraine off from the sea on Thursday via its key southern ports, claiming the capture of Kherson and tightening the siege of Mariupol, as a large amphibious taskforce threatened Odesa to the west.
With the Russian naval assault in the south spreading, a second merchant ship – the Estonian-owned carrier Helt – was hit and sunk after a Bangladeshi-owned cargo ship had been hit by a projectile that killed one of its crew.
The ports, spread along hundreds of miles of Ukraine’s coastline, running from the Sea of Azov in the east to the Black Sea, have become an increased focus of attention for Russian forces in recent days – as it has become clear that the latest phase of the Russian invasion plan is seeking to cut off and isolate large sections of the country.
Cutting Ukraine’s access to its coast would deal a crippling blow to the country’s economy and allow Russia to build a land corridor stretching from its border, across Crimea, which has been occupied by Russia since 2014, and all the way west to Romania.
Another key objective for Russian forces in the south east appeared to be Zaporizhzhia and its nuclear power plant in south-eastern Ukraine, Europe’s biggest, where Russian troops were trying to break through a barricade to the plant erected by local residents and territorial defence forces.
The moves in the country’s south have come as Russia forces have attacked the country in three directions, seeking to stretch Ukraine’s armed forces and damage their ability to respond.
In the latest threat to Ukraine’s coastline, residents told the Guardian they were stepping up preparations to defend it against a potential Russian marine landing, amid sightings of a convoy of Russian warships, and US warnings that an amphibious assault on Odesa – Ukraine’s biggest port – would be an economic catastrophe for Ukraine.
Residents in the city told the Guardian of a marked increase in Russian airstrikes on Wednesday as images emerged of beaches close to the city laid with mines, and other defences being prepared.
Concern surrounding a potential amphibious landing targeting Odesa mounted on Thursday following images of a Russian naval convoy showing at least eight ships visible off the coast.
The convoy appears to include a number of 4,080 tonne Ropucha-class large landing ships and supporting vessels.
The south has seen some of Russia’s biggest military gains during the week-old war so far, with the capture of Kherson, on the Dnieper River, opening the way for the assault on Odesa as well as for Russian forces to push north.
Describing the fall of Kherson as representing a major strategic loss for Ukraine’s defenders, Michael Clarke of the Royal United Services Institute said Russian forces were attempting to build “a land bridge” across the southern territory which he suggested they would then ultimately attempt to link to the northern front around the capital Kyiv.
“Kherson is very important because it is the city that controls the water supply to the Crimea,” said Clarke in an online briefing.
“It’s also the city that’s key to crossing the Dnieper River. And at some point the Russians will want to be on both sides of the river to move up and join up with their northern front. Kherson is a big gain for [the Russians]. It’s taken them a while but they are here now.”
Mykolaiv’s regional governor, Vitaliy Kim, said that big convoys of Russian troops were advancing on that city, which is another major Black Sea port and shipbuilding centre to the west.
In Kherson itself, the regional governor, Hennadiy Lahuta, conceded Russians were in the city but added that his staff had “not given up our duties”. A US defence official said it was too early to say whether Russian forces were in full control of Kherson.
Kherson’s mayor, Ihor Kolykhaiev, said in a Facebook post early on Thursday that Russian troops were in control of the city hall and that residents should obey a curfew imposed by what he called the “armed visitors”.
Kolykhaiev said he had made “no promises” to the Russian forces and that he was “only interested in the normal life of our city. I just asked [them] not to shoot people.”
Reports also emerged from Mariupol that Russian forces were attempting to prevent civilians from evacuating, according to the mayor, Vadym Boichenko.
Heavy fighting continued on the outskirts of Mariupol, with electricity and phone services largely cut, and homes and shops facing food and water shortages.
Boichenko said in a video broadcast: “The invaders are systematically and methodically trying to blockade the city of Mariupol.”
While Russia troops were advancing in the south, in the north of the country a war of attrition continued around the capital Kyiv where a massive Russian convoy to the north west, which earlier in the week had seemed poised to launch an assault on the capital, appeared stalled.
“Kyiv withstood the night and another missile and bomb attack,” said the Ukrainian president, Volodymyr Zelenskiy.
“Our air defences worked,” he said. “Kherson, Izyum — all the other cities that the occupiers hit from the air did not give up anything.”
In a video address to the nation early Thursday, Zelenskiy praised his country’s resistance.
“We are a people who in a week have destroyed the plans of the enemy,” he said. “They will have no peace here. They will have no food. They will have here not one quiet moment.”
He said the fighting is taking a toll on the morale of Russian soldiers, who “go into grocery stores and try to find something to eat”.
“These are not warriors of a superpower,” he said. “These are confused children who have been used.”
Kyiv’s mayor, Vitali Klitschko, said explosions heard overnight in the Ukrainian capital were Russian missiles being shot down by air defence systems.