Vladimir Putin has ramped up his threats against Ukraine and its allies with a warning that any attempt to impose a no-fly zone over Ukraine would be considered an act war.

The Russian president also said tough international sanctions which have been introduced against his country were the “equivalent of a declaration of war.”

Of the no-fly zone, Mr Putin told a meeting of female Russian flight crew members, which was broadcast on state television: “Any movement in this direction will be considered by us as participation in an armed conflict by that country.”

The West has so far not heeded pleas from Ukraine’s President Volodymyr Zelensky for a no-fly zone over the country’s air space to hamper Russian military planes.

NATO chief Jens Stoltenberg said while it understood Ukrainian requests, this would involve shooting down Russian planes which could lead to a “full-fledged” war in Europe.

Mr Putin also warned of the consequences of Ukraine joining NATO.

“We begin to talk more and more actively about the fact that Ukraine will be accepted into NATO. Do you understand what this could lead to?” he said.

While explaining the motives behind Russia’s “special military operation” in its smaller neighbour, the Kremlin leader said the decision to enter Ukraine was a “difficult” one.

“I said it at the beginning of the operation and before this decision was taken. It was a difficult decision, without a doubt,” Mr Putin said.

Civilians trapped as ceasefire broken

Citizens continue to evacuate bombarded Ukraine and head west. Photo: Getty

Russia has been accused of breaking a ceasefire designed to allow citizens to escape safely from two Ukraine cities besieged and bombarded by invading forces.

Humanitarian corridors were meant to be opened near the cities of Mariupol and Volnovakha, which have been encircled by Russian  troops.

But in Mariupol, the city council said Russia was not observing the ceasefire and it asked residents to return to shelters and await further information.

Russia’s defence ministry accused Ukrainian “nationalists” of preventing civilians from leaving.

Since Russia’s invasion 10 days ago, some 1.5 million refugees have fled westward, Europe’s biggest humanitarian disaster in decades.

Russia and Ukraine have blamed each other for a failure to provide safe passage to the civilians fleeing the two encircled cities of Mariupol and Volnovakha.

The International Committee of the Red Cross said it understood that relocation of civilians would not start on Saturday because of the conflict.

“We remain in dialogue with the parties about the safe passage of civilians from different cities affected by the conflict,” the ICRC said.

“The scenes in Mariupol and in other cities today are heart-breaking.

“Any initiative from the parties that gives civilians a respite from the violence and allows them to voluntarily leave for safer areas is welcome.”

The Ukrainian government said the plan was to let about 200,000 people leave Mariupol and 15,000 to depart Volnovakha.

Only 17 people left Mariupol on Saturday and no one had left Volnovakha, Tass cited pro-Russian separatists as saying.

Ukrainian servicemen assist a woman and child trying to escape. Photo: Getty

The Russian defence ministry said a broad offensive would continue in Ukraine, where it denies targeting civilians.

Officials in Ukraine have reported thousands of dead and wounded people.

Russia says its aim is to disarm its neighbour, counter what it views as NATO aggression and capture leaders it calls neo-Nazis.

On Saturday it accused the US and its allies of acting like a bandit and threatened to retaliate without giving details.

“As you understand, there must be a corresponding response to economic banditry,” Kremlin spokesman Dmitry Peskov said.

Third round of peace talks

Russia and Ukraine will hold a third round of talks about ending hostilities, Ukrainian negotiator David Arakhamia says.

Ukraine said previous talks had not produced results but that it would keep pursuing negotiations.

“The third round of talks will take place on Monday (local time),” said Mr Arakhamia.

The Kremlin said on Friday that progress in the negotiations would depend on Ukraine’s reaction to Russia’s position on how to end the war, which had been conveyed to Kyiv officials on Thursday.

Israel and Turkey step in

Israel, home to a substantial population of Russian immigrants, has offered to mediate in the conflict although officials have previously played down expectations of a breakthrough.

Israeli Prime Minister Naftali Bennett.

Israeli Prime Minister Naftali Bennett met with Mr Putin in Moscow to discuss the Ukraine crisis.

Mr Bennett’s office said the meeting lasted two and a half hours.

While Israel — a close ally of the United States — has condemned the Russian invasion, voiced solidarity with Ukraine and sent humanitarian aid to Kyiv, it has said it will maintain communications with Russia in the hope of helping to ease the crisis.

Israel is also mindful of Russia’s military support for President Bashar al-Assad in next-door Syria, where Israel regularly attacks Iranian and Hezbollah military targets.

Turkish President Tayyip Erdogan is due to meet Mr Putin and tell him to stop Russia’s invasion of Ukraine, an Erdogan spokesman said.

NATO member Turkey shares a maritime border with Ukraine and Russia in the Black Sea and has good ties with both countries.

Turkey has opposed sanctions on Russia but also described its invasion of Ukraine as unacceptable, called for a ceasefire and offered to host peace talks.

-with AAP