KYIV (AFP, REUTERS) - Ukraine’s President Volodymyr Zelensky warned on Sunday (March 6) that Russian forces are preparing to shell Odessa, a historic port city on the Black Sea coast.

"They are preparing to bomb Odessa. Odessa!" he declared in a video address.

"Russians have always come to Odessa. They have always felt only warmth in Odessa. Only sincerity. And now what? Bombs against Odessa? Artillery against Odessa? Missiles against Odessa?" he demanded. 

"It will be a war crime. It will be a historical crime." 

Russian forces have made progress in southern Ukraine since their Feb 24 invasion, overrunning the city of Kherson and besieging the port of Mariupol, but Odessa has so far been largely spared.  

Almost a million people live in Odessa, a cosmopolitan harbour on Ukraine’s southern coast with both Ukrainian and Russian speakers and Bulgarian and Jewish minorities.

The Russian advance from occupied Crimea has in part turned east to link up with Russian-backed separatists and to seize the Azov Sea port of Mariupol.  

But another part of the force has also headed west to Kherson, on the road towards Odessa. The city is also close to the Moldovan border and the Russian-occupied region of Transnistria. 

Mariupol fails again to evacuate civilians

The Ukrainian port city of Mariupol, which is surrounded by Russian troops, said it will restart efforts to evacuate civilians on Sunday, after earlier efforts were scuppered by ceasefire violations.

"From 1200 (1000 GMT) the evacuation of the civilian population begins," city officials announced in a statement, which said a ceasefire was agreed with Russian-led forces surrounding the city.

But pro-Russian separatists and Ukraine’s National Guard later on Sunday accused each other of failing to establish a humanitarian corridor out of the city.  

Ukraine 24 television showed a fighter of the Azov Regiment of the National Guard who said Russian and pro-Russian forces that have encircled the port city of about 400,000 continued shelling the areas that were meant to be safe.  

The Interfax news agency cited an official of the Donetsk separatist administration who accused the Ukrainian forces of failing to observe the limited ceasefire.  

The Donetsk official said only about 300 people have left the city. The Ukrainian authorities had earlier said they planned to evacuate over 200,000 people from Mariupol.

An earlier attempt on Saturday to allow civilians to leave by buses and private cars along the road north-west towards Zaporizhzhia also failed when both sides accused each other of shelling.

According to aid agency Doctors Without Borders (MSF), the humanitarian situation in Mariupol, a key target for the Russian invasion forces, is "catastrophic" with no power or water in civilian homes.

"It is imperative that this humanitarian corridor... is put in place very quickly," MSF's emergency coordinator in Ukraine, Ms Laurent Ligozat, told AFP.

The Ukrainian authorities accused the Russians of shelling even when civilians were gathering to form an escape convoy, but Moscow's Defence Ministry accused the city's defenders of exploiting a "human shield".

Separately, on Sunday, the head of the Kyiv-controlled Luhansk regional administration said a train would be organised to evacuate women, children and the elderly from Lysychansk.

Lysychansk is near the front line between Ukrainian forces and Moscow-backed separatists, who are fighting to link up with the Russian forces and control the entire south-east.

"You need to reach Lysychansk station on your own. Women with children are boarding first, then women under 40, women, the elderly," Mr Sergiy Gaiday wrote on Telegram.

If Russian forces succeed in capturing Mariupol, which held out against rebel forces in the previous 2014 conflict, they will control Ukraine's entire Azov Sea coast.

This would give them a land bridge from Russia to Russian-annexed Crimea and an important supply route and port if they decide to push north in a bid to take all of eastern Ukraine.

During the first 11 days of the conflict, Russian forces from Belarus have also advanced on the capital Kyiv from the north-west and north-east, while another group bombarded the northern city of Kharkiv.

Several cities have been bombed and shelled and the United Nations estimates that more than a million civilians have been driven from their homes by the fighting.

Follow The Straits Times' live coverage on the Ukraine crisis here.