He added Russian saboteurs were being regularly rounded up. Zelensky called for tougher sanctions on Russia,including closing all ports and airports to Russian vessels and planes,and for countries to cease paying for Russian energy exports.

“Buying Russian goods now,is to pay money for murdering people,” Zelensky said.

British intelligence,released by the Ministry of Defence on Tuesday,said the Russian advance on Kyiv had made little progress over the past 24 hours,most likely as a result of continuing logistical difficulties.

Russian forces have increased their use of artillery north of Kyiv and in vicinities of Kharkiv and Chernihiv,with the use of heavy artillery in densely populated urban areas greatly escalating the risk of civilian casualties.

Ukrainian presidential adviser Oleksiy Arestovych said Russian forces were trying to lay siege to Kyiv and Kharkiv.

Russian troops fired artillery at Kyiv,Kharkiv and the southern port city of Mariupol overnight while the Ukrainian side shot down Russian military planes around the capital,Arestovych said in a televised briefing.

He described the current situation as under control. The mayor of Mariupol said on Tuesday morning that the southern port city was under constant shelling,which had killed civilians and damaged infrastructure.

“We have had residential quarters shelled for five days,” Vadym Boichenko said in a live broadcast on Ukrainian TV. “We have civilian infrastructure damaged - schools,houses. There are many injured. There are women,children killed.”

Throughout the country,many Ukrainian civilians spent another night huddled in shelters,basements or corridors. The UN refugee agency says more than 660,000 refugees have fled Ukraine to neighbouring countries in the past six days.

UK Defence said Russia had failed to gain control of the airspace over Ukraine,prompting a shift to night operations in an attempt to reduce their losses. Few details have been released on the peace discussions,except that a second round could take place “in the near future”.

Ukraine’s leader Zelensky called for an international tribunal to investigate Russia for its actions in recent days,which he described as war crimes. The bombardment of a residential area,which may have included cluster munitions that are banned by most nations,killed at least nine civilians and wounded dozens.

“Russian troops shelled Kharkiv using rocket artillery,” he said in a video posted to his social media. “This is,without any doubt,a military crime. A peaceful city. Peaceful residential neighbourhoods. Not a single military object in sight.

“For such a crime,there needs to be a tribunal. An international one. This is a violation of all conventions. No one in the world will forgive you for the murder of peaceful Ukrainian people. This is Ukraine. This is Europe. This is the year 2022. Evil,armed with rockets,bombs and artillery,must be stopped immediately.”

Ukrainian officials said 16 children had been killed in the first four days of fighting,but that number is likely to have risen significantly in the past 24 hours,after the deadliest attacks on civilians since the start of the invasion.

Among the dead was schoolgirl Polina,who was killed by Russian saboteurs in Kyiv along with her parents and brother,according to officials.

Russia has previously deployed the banned weapon,also known as an aerosol bomb,in Chechnya and Syria. Cluster munitions scatter or release smaller munitions or bomblets over a wide area,increasing the potential for casualties and damage.

Putin’s decision to invade Ukraine last week was expected to be a quick victory over a smaller and outgunned adversary. But it has inspired widespread resistance with many Ukrainians staying put to try to thwart the invaders.

UN human rights chief Michelle Bachelet said her office has confirmed that 102 civilians,including seven children,have been killed in the Russian invasion and 304 others wounded in Ukraine since Thursday. She cautioned that the official tally was likely vastly lower than the reality.

Moscow is facing widespread opposition internationally and has become increasingly isolated as the United States,Britain,France and its allies expand economic sanctions on Russia and on Putin’s allies.

Switzerland is the latest traditionally neutral nation to have joined the growing sanction regime,by freezing Russian financial assets,while Israel is poised to join a vote condemning Russia at the United Nations. Jerusalem has long been cautious in its dealings with Moscow,due to the presence of Russian forces in Syria that co-ordinate with Israel,as well as the large number of Jews in Ukraine.

The chief prosecutor of the International Criminal Court,Karim Khan,said he intends to open an investigation into alleged war crimes.

He said in a statement the investigation would look at alleged crimes committed before the recent Russian invasion,but added that “given the expansion of the conflict in recent days,it is my intention that this investigation will also encompass any new alleged crimes falling within the jurisdiction of my office that are committed by any party to the conflict on any part of the territory of Ukraine”.

The European Union is warning more than 7 million Ukrainians could flee their homes,leading to a wave of refugees that would dwarf the 2015 migration crisis and rival the turmoil that followed World War II,when more than 12 million people were displaced.

At least 500,000 Ukrainians have crossed west into neighbouring countries since the start of the fighting,the UN refugee agency said. An estimated 120,000 are thought to have moved to Russia from Russian-occupied territory in the south-east of the country. About 160,000 have gone to Poland,which could accept as many as 1.5 million refugees over the crisis.

Prime Minister Scott Morrison announced on Tuesday Australia would send a $105 million package of weapons along with humanitarian assistance to Ukraine. About $70 million of defensive support would be provided to Ukraine,which would include missiles and ammunition. A further $35 million would be spent on humanitarian assistance such as shelter,food and medical care.

Get a note directly from our foreigncorrespondentson what’s making headlines around the world.Sign up for the weeklyWhat in the World newsletter here.