Russia targets Ukrainian military base near Polish border in escalation

Sullivan said the US was consulting allies and in contact with the Kremlin directly to warn against the use of chemical weapons amid fears that Russia may be preparing the ground for the use of them.

The Ukrainian president, Volodymyr Zelenskiy, said in a video address that a convoy carrying 100 tons of humanitarian aid was on its way to the city, where more than 2,000 civilians have died, and that all necessary diplomatic efforts had been taken to make sure it reaches those in need.

The Yavoriv facility hit by Russia on Sunday has previously hosted foreign military trainers from the UK, US and other countries, but it was not clear whether any were at the base. Ukraine held most of its drills with Nato countries there before the invasion, with the last major exercises in September. Nato denied it had any personnel in Ukraine and the Pentagon said its last people had left weeks ago.

The attack is thought to be the westernmost carried out by Russia in 18 days of fighting.

As Sunday wore on, heavy fighting continued on multiple fronts across the country, including the southern shipbuilding centre of Mykolaiv, where authorities reported nine people killed in bombings as Russian forces attempted to bypass the city en route to Odesa.

Around the capital, Kyiv, a major political and strategic target for the invasion, fighting intensified, with overnight shelling in the north-western suburbs and a missile strike on Sunday that destroyed a warehouse in the east.

Brent Renaud, an award-winning US film-maker whose work has appeared in the New York Times and other outlets, was killed by Russian forces in the flashpoint town of Irpin, near Kyiv. A US photographer, Juan Arredondo, was wounded.

Despite the violence, both sides said they thought progress could be made at bilateral talks that have been held periodically since Russia invaded on 24 February, although they gave no details of what might be agreed.

A Russian delegate to the talks with Ukraine, Leonid Slutsky, was quoted by the RIA news agency as saying they had made significant progress and it was possible that the delegations could soon reach draft agreements.

Neither side said what these would cover. Three rounds of talks between the two sides in Belarus, most recently last Monday, had focused mainly on humanitarian issues.

In Russia, more than 800 people were detained by police for protesting against its invasion of Ukraine. OVD-Info, which monitors arrests during protests, said police had detained 817 people during demonstrations in 37 cities in Russia.