Demonstrators chanting "refugees are welcome here" have marched through London to persuade the government to resettle more refugees in the UK.
Organisers said they hope the prime minister will "lead an appropriate humanitarian response" to the crisis at a UN refugee summit next week.
The demonstration follows news that the UK is on track to resettle 20,000 refugees by 2020.
The UN says 4.5m Syrians have fled their homes during the country's war.
Groups such as Oxfam, Medecins Sans Frontieres, Amnesty International, the Refugee Council and Stop the War Coalition collaborated for the demonstration, organised by charity coalition Solidarity with Refugees.
During the march, protestors carried flags and placards, and chanted: "Theresa May, you will say, refugees are welcome here", and refugees, celebrities and religious leaders spoke at a rally in Parliament Square.
Actor and campaigner Vanessa Redgrave said at the rally: "The present government and previous governments, both Labour, coalition and Conservative, have been breaking international human rights law. We must hold them to account."
Home Secretary Amber Rudd said earlier this month that the government had received enough pledges of available accommodation from local authority housing departments for the government to meet its target to resettle 20,000 refugees under the Vulnerable Persons Relocation Scheme.
Under the scheme, the government will pay £8,500 towards housing, healthcare and other costs for each refugee in the first year, but this figure is reduced to £1,000 by the fifth year.
But Solidarity with Refugees director Ros Ereira said the current response had been slow.
"The situation is growing, it is not decreasing - it is not going away and there are people dying and we need to stop that happening," she said.
She hopes Prime Minister Theresa May will "set the tone" for her leadership and play "an important role on the global stage" at next week's UN Summit for refugees and migrants in New York, hosted by US President Barack Obama.
Refugee Kais Aldahou, 24, who came to the UK from Damascus in Syria in 2009 to study at university, said: "It is about more support, not necessarily bringing in more refugees, but to help the camps around Europe - the situations in them are pretty horrendous."
This year's UN annual report for World Refugee Day revealed the number of refugees worldwide had passed 60 million for the first time, with more than half coming from Syria, Afghanistan and Somalia.