Negotiators from Ukraine and Russia have resumed their talks amid deadly Russian assaults on Ukraine's cities.

The talks come as Russian forces step up offensives across Ukraine.

They are closing in on Kyiv from three directions. They also attacked a military facility in the west of the country with missiles.

Attacks on the southeastern city of Mariupol are intensifying.

Russia apparently wants to take control of the region to secure a supply route to Crimea, which it annexed in 2014.

The British Defence Ministry said on Sunday that Russian naval forces had established a blockade of Ukraine's Black Sea coast, effectively isolating the country from international maritime trade.

Ukraine's Foreign Minister Dmytro Kuleba tweeted on Sunday that Russian troops had abducted the mayor of Dniprorudne, a city in the southeastern region of Zaporizhzhia.

Last Friday, the Ukrainian government announced that Russian troops had abducted the mayor of Melitopol.

EU foreign policy chief Josep Borrell called the abductions attacks on democratic institutions in Ukraine.

He accused Russia of trying to establish illegitimate alternative government structures in a sovereign country.

Russian and Ukrainian talks on Monday were being held by video link.

A Russian negotiator reportedly said on Sunday that significant progress had been made and could lead to an agreement within a few days.

The Ukrainian side says Russia has begun to speak constructively.

Ukrainian President Volodymyr Zelenskyy says the task of his delegates is to do everything possible to ensure that a Ukraine-Russia summit will take place.

He said, "This is a complicated situation. It's a difficult path, but a necessary path, and our goal is to ensure that Ukraine gets the necessary result from this struggle, from this difficult negotiation work."

The steady flow of refugees out of Ukraine continues. The UN refugee agency says more than 2.8 million people have fled.

About 60 percent of them crossed into Poland.

In Russia, demonstrators continue to protest the invasion. Human rights monitors in the country say about 15,000 people have been detained.

Information has emerged suggesting possible discord in the Russian government.

Local independent media report that the head of the international intelligence unit of the FSB -- Russia's federal security service -- may have been placed under house arrest.

Local media say the FSB official was responsible for reporting to President Vladimir Putin on the situation in Ukraine prior to the invasion.

Reports say the official was telling Putin only what he wanted to hear, out of fear of making him angry, but that two weeks into the war, the president finally noticed that he had been misled.

The information in the reports has not been verified.

Meanwhile, officials from the US and China have sat down for talks in Rome to discuss the conflict.

US National Security Advisor Jake Sullivan appears to be trying to ensure China will not help Moscow evade punishing sanctions by offering financial or material help.

That could include military assistance.

Various outlets say unnamed US officials have confirmed that Moscow has been looking to Beijing for backup in efforts to break through Ukrainian resistance.

Beijing flatly denies such allegations.