Two British nationals have gone missing in the eastern Donetsk region of Ukraine, Ukrainian police have said.
Andrew Bagshaw, 48, and Christopher Parry, 28, were doing voluntary work, police said, and were last seen on Friday heading to the town of Soledar – where fighting has been intense.
The Foreign Office said it was "supporting the families".
Mr Bagshaw's parents said they "love him dearly" and were "immensely proud of all the work he has been doing".
There has been no contact with the two men since Friday.
Mr Parry, from Truro in Cornwall, travelled to Ukraine to do humanitarian work and had most recently been helping people evacuate Bakhmut, in the eastern Donbas region.
Speaking to BBC Cornwall from Ukraine over Christmas last year, he described having a "drive to help, as the people here are so lovely".
He spoke about the "continuous" bombardment as he spent time near the front line, as well as encountering a drone "within about 10 metres of my face".
Mr Parry, who lives in Cheltenham, has written in his online crowdfunding page about raising money for vehicle repairs, fuel and equipment to help evacuate civilians, and gave examples of helping children and families to flee the front line.
In a statement issued to the media in New Zealand – where Mr Bagshaw lives – his parents described the work he has been doing "delivering food and medicines and assisting elderly people move from near the battlefront of the war".
The police department in the city of Bakhmut said they received a missing person's report at 17:15 local time on Saturday, and appealed for any information that could help locate the two men.
The men had been in Kramatorsk, where there have been reports of strikes in recent days.
They were last seen heading to the small, eastern town of Soledar. The UK's Ministry of Defence said on Tuesday that Russia was "likely" in control of most of Soledar after a months-long battle with Ukrainian forces.
The British Foreign Office is warning against all travel to Ukraine due to attacks on a number of different cities currently taking place, as the war continues into its 11th month.
It says there is a "real risk to life", adding British nationals still in Ukraine should leave immediately.
There have been several cases of Britons going missing or being captured in Ukraine over the last year.
Last September, five British nationals who were being held by Russian-backed forces were released after Saudi Arabia said it had brokered an exchange between Russia and Ukraine of 10 detainees.
This meant Aiden Aslin, John Harding, Dylan Healy, Andrew Hill and Shaun Pinner were all allowed to return home following months of capture.
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