London Ukraine demo demands 'Stop Putin, stop the war'
The large crowd gathered on the central Trafalgar Square, singing the national anthem while draped in Ukrainian flags and calling Russian President Vladimir Putin a "terrorist".
"When the last Ukrainian soldier falls, Putin will come for you ladies and gents," read a giant banner.
"I'm Ukrainian and I still have some family and friends in Ukraine," said Olena Marcyniuk, 36, at the protest with her children aged 14 months and nine years.
"We need to keep on reminding everyone, we need to stay united to support our country," she told AFP, with a Ukrainian flag around her waist and on her pram.
"Maybe somehow (we can) get through to Russia as well that the world is for Ukraine and that it needs to start acting to stop the war."
She said much of her family had fled but that her uncle stayed in Kyiv to "fight for the city".
Papal nuncio to Great Britain Archbishop Claudio Gugerotti led a prayer, saying "Today we are all Ukrainians."
"Stop Putin, stop the war," read a placard.
"My mother and my step-dad and all my friends are in (eastern Ukrainian city) Sumy where they've been bombed, shelled for the last two days," said Natalya Courtney, 41.
"At this moment I'm actually waiting for my mother to reply to me to find out if she's okay," said the school finance manager.
"It's just important for me that we win this war and get our freedom back... it's just horrific," she said as rain began to fall.
"We're doing all we can to help with sending money, collecting parcels, collecting medical aid for soldiers, so whatever we can, but it's just really, really stressful, very upsetting."
She called for NATO to establish a no-fly zone over Ukraine, something the West has refused to do for fear of escalating the conflict.
"Just help us help us to win the war on the ground because it's the shelling of innocent civilians, children, women, elderly people... It's just a massacre."