(Adds British defence ministry intelligence assessment)
Zelenskiy says no walls left standing in Soledar
Britain says Russian forces may control most of town
Wagner Group sending waves of fighters, Ukraine says
Fight for cavernous salt mining tunnels beneath town
By Pavel Polityuk and Vladyslav Smilianets
KYIV/SIVERSK, Ukraine, Jan 10 (Reuters) - Russian troops have stepped up an assault on the town of Soledar in eastern Ukraine, forcing Ukrainian troops to repel waves of attacks led by mercenary forces, officials in Kyiv said.
Britain's defence ministry said on Tuesday that Russian and forces of the Wagner contract group were probably now in control of most of the small salt mining town after advances in the last four days.
Soledar, in the industrial Donbas region, lies a few miles from Bakhmut, where troops from both sides have been taking heavy losses in some of the most intense trench warfare since Russia invaded Ukraine nearly 11 months ago.
"Russia's Soledar axis is highly likely an effort to envelop Bakhmut from the north, and to disrupt Ukrainian lines of communication," Britain said in an intelligence briefly.
Ukrainian President Volodymyr Zelenskiy said in his nightly video address on Monday that Bakhmut and Soledar were holding on despite widespread destruction.
He cited new and fiercer attacks in Soledar, where he said no walls have been left standing and the land was covered with Russian corpses.
"Thanks to the resilience of our soldiers in Soledar, we have won for Ukraine additional time and additional strength," Zelenskiy said. He did not spell out what he meant by gaining time or strength.
Russia's defence ministry did not mention either Soledar or Bakhmut in a media briefing on Monday.
Wagner was founded by Yevgeny Prigozhin, an ally of Russian President Vladimir Putin. Drawing some recruits from Russia's prisons and known for uncompromising violence, it is active in conflicts in Africa and has taken a prominent role in Russia's war effort in Ukraine.
WAVES OF ATTACKS
Prigozhin has been trying to capture Bakhmut and Soledar for months at the cost of many lives on both sides.
He said on Saturday its significance lay in a network of cavernous mining tunnels below the ground, which can hold troops or tanks.
A U.S. official has said Prigozhin was eyeing the salt and gypsum from the mines, believed to extend over 100 miles underground and contain auditorium-scale caverns.
Ukrainian military analyst Oleh Zhdanov said fighting in Bahkmut and Soledar was "the most intense on the entire frontline".
"So many remain on the battlefield ... either dead or wounded," he said on YouTube.
"They attack our positions in waves, but the wounded as a rule die where they lie, either from exposure as it is very cold or from blood loss. No one is coming to help them or to collect the dead from the battlefield."
Reuters could not immediately verify battlefield reports.
In an evacuee centre in nearby Kramatorsk, Olha, 60, said she had fled Soledar after moving from apartment to apartment as each was destroyed in tank battles.
"There isn't one house left intact. Apartments were burning, breaking in half," said Olha, who gave only her first name.
APPEAL FOR WEAPONS
Ukrainian officials, led by the commander in chief General Valery Zaluzhniy, have warned that Russia is preparing fresh troops for a new offensive on Ukraine, possibly on the capital Kyiv.
Zelenskiy also appears to be banking on securing more, sophisticated weapons from Ukraine's Western partners to beat off attacks and eventually expel Russian troops.
On Monday, he pressed on with diplomatic efforts, speaking to Petr Fiala, Prime Minister of the Czech Republic.
"I am certain that our soldiers at the front will get these weapons and equipment. Very soon," he said.
France, Germany and the United States all pledged last week to send armoured fighting vehicles, fulfilling a long-standing Ukrainian request. Britain is considering supplying Ukraine with tanks for the first time, Sky News reported, citing a Western source. Britain's Defence Ministry did not comment.
(Reporting by Reuters bureaus; Writing by Michael Perry and Alex Richardson; Editing by Himani Sarkar and Angus MacSwan)