The British embassy in the Ukrainian capital Kyiv will reopen next week, Boris Johnson has announced.

Ambassador Melinda Simmons said she was "heading back" after leaving when Russia invaded.

The prime minister also said there was a "realistic possibility" the Russian bombardment would continue until the end of next year.

Mr Johnson added the UK was looking at sending tanks to support Poland as it supplies Ukraine with heavy weaponry.

The prime minister made the embassy announcement at a news conference in Delhi, where he has been holding talks with Indian leader Narendra Modi.

It comes after Russia withdrew forces from around Kyiv when it failed to seize the capital, and launched an assault on the eastern Donbas region.

Mr Johnson visited Kyiv earlier this month to meet President Volodymyr Zelensky, following a pledge to give £100m worth of weapons to Ukraine.

Taking questions from reporters, the prime minister said intelligence assessments that the Russian assault could continue to the end of next year, and end with a Russian victory, were plausible.

He said Russian President Vladimir Putin has "a huge army" but "he has a very difficult political position because he's made a catastrophic blunder".

Mr Johnson said: "The only option he now has, really, is to continue to try to use his appalling, grinding approach driven by artillery, trying to grind the Ukrainians down.

"I think no matter what military superiority Vladimir Putin may be able to bring to bear in the next few months, and I agree it could be a long period, he will not be able to conquer the spirit of the Ukrainian people."

The prime minister said he was looking at what the UK could do to "backfill" weapons in countries, such as Poland, "who may want to send heavier weaponry to help defend the Ukrainians".

"We're looking at sending tanks to Poland to help them, as they send some of their T-72s [tanks] to Ukraine and other steps like that," Mr Johnson said.

Sending British main battle tanks to Poland, if confirmed, would be a very significant move.

As one senior British Army officer put it, it raises the UK's commitment to Ukraine by a further notch but also increases the chances of Britain - and Nato - eventually becoming co-belligerents in this conflict.

The tanks, which the Ministry of Defence says would be Challenger 2 main battle tanks, would be intended to "backfill" for Poland's T72 tanks, which it is sending directly to Ukraine. There are no plans to send British tanks or crews into action in Ukraine.

Until very recently Nato countries have been reluctant to supply heavy weaponry to the Ukrainians for fear of antagonising President Putin and risking an all-out European war that puts Nato forces into direct conflict with Russia.

But with each reported Russian atrocity that is revealed, notably in Bucha, these Western inhibitions have melted away.

Poland is sending tanks, Slovakia has sent its S300 air defence missiles and the US is sending powerful, long-range 155mm artillery.

For Ukraine's army, outnumbered and outgunned in the eastern Donbas region, such help cannot come quickly enough.

But President Putin has made no secret of his irritation at Nato's assistance to his enemy and he used this week's test-launch of a nuclear-capable missile to remind the West of Russia's massive arsenal of strategic nuclear weapons.

In the long term, Mr Johnson said he believed Western nations would respond to demands from Ukraine to guarantee the country's security against future attacks.

He said this would not replicate the Article 5 guarantee for Nato members - in which an attack on one country is treated as an attack on all members.

But instead, Western allies would offer pledges to provide weaponry, training and intelligence-sharing, the prime minister said.

"I hope it will enable the Ukrainians to offer deterrents by denial and to make sure their territory is so fortified as to be impregnable in the future to further attack from Russia," he said.

"Deterrence by denial" is a term in military thinking which means seeking to put off an aggressor by making their attack infeasible or unlikely to succeed, rather than through the threat of retaliation.

Mr Johnson added that he backed ministers if they chose to visit the embassy.

European diplomats have also been returning to the capital.