Britain should "do much more" to assist in the current migration crisis, the Secretary General of the United Nations has said.
Ban Ki-moon said he had urged Prime Minister David Cameron to show "compassionate leadership" on the issue, pointing out that Britain is one of the world's richest countries and has benefited from immigration in the past.
Britain is already the second largest bilateral donor to support displaced people in Syria and neighbouring countries, giving a total of more than £1 billion, and Mr Cameron announced earlier this week that the UK will admit a further 20,000 vulnerable people from refugee camps in the region.
But Mr Cameron has made clear that the UK will not take part in a European Commission plan to resettle 160,000 migrants who have arrived in Italy, Greece and Hungary over recent months.
Speaking to ITV News, Mr Ban welcomed the resettlement plan announced by Commission President Jean-Claude Juncker on Wednesday, adding: "I should hope the UK will also do the same."
And he said: "I have spoken to Prime Minister David Cameron and urged him to show strong global leadership and compassionate leadership because (the) United Kingdom is also a country which has benefited through immigration and migration.
"Therefore, as one of the permanent members of the Security Council, one of the richest countries, there is a heightened expectation that the UK should do much more."
If the international community failed to address the Syrian crisis as soon as possible, "we may have to regret that we have made a complete failure," said the UN chief.
He warned that world leaders "have not been united, they have not been showing unity of purpose", adding: "I sincerely hope that we must be united this time and address the root causes.
"But before that, we have to address these life-saving missions and that's why I'm appealing to EU leaders. EU leaders, individually and collectively, they are the group of countries that are most well-to-do, richest countries in the world at this time, therefore they have the capacity to show compassionate leadership. And as Secretary General, that's the issue which keeps me up during the night."
The "needless death" of three-year-old Aylan Kurdi should prompt Europe to "rise against this crisis", he said.
Describing his own reaction to seeing pictures of the Syrian boy's body on a Turkish beach after he drowned with his mother and brother trying to reach Greece, Mr Ban said: "I was heartbroken. That's why I made my personal appeal to the world leaders, particularly European leaders.
"This is a needless death. When there is war, it's always women and children, the vulnerable people whose lives are always threatened, whose lives are always first to be victimised. We have to rise against this crisis."
Home Secretary Theresa May and Communities Secretary Greg Clark are on Friday meeting local authority and charity representatives at the first session of a committee set up to plan practical arrangements for Britain to take in 20,000 Syrian refugees over the next five years.