NEW YORK — World leaders will gather for their annual meeting at the United Nations starting tomorrow as Europe faces a flood of asylum seekers, many fleeing Syria’s civil war in the worst humanitarian crisis since the world body was created 70 years ago.

Islamic State will also top the agenda, with American President Barack Obama hosting a counter-terrorism meeting and Russian Foreign Minister Sergei Lavrov chairing a high-level UN Security Council meeting on counterterrorism.

Before the marathon of speeches in the 193-member General Assembly starts on Monday, Pope Francis — a strong advocate for action to combat climate change — will address the UN tomorrow ahead of a three-day summit that will formally adopt a global sustainable development agenda for the next 15 years.

“General Assembly high-level week is always known as diplomatic speed-dating, but I think this year is breaking records,” said the US Ambassador to the United Nations, Samantha Power.

The leaders making rare appearances at the United Nations’ 70th anniversary include German Chancellor Angela Merkel, Cuban leader Raul Castro, and Russian President Vladimir Putin.

Mr Xi Jinping, who is in the United States for an official visit this week, will also make his UN debut as China’s President.

The new sustainable development agenda, which was agreed on by UN members last month, aims to wipe out hunger and extreme poverty, reduce inequality within and between countries, achieve gender equality, improve water management and energy, and urgently combat climate change.

Mr Putin is expected to use the UN platform to speak about the need for countries to join together to destroy Islamic State and tackle the threats posed by extremism and terrorism. While he has no formal meeting planned with Mr Obama, there will be opportunities for the two to speak on the sidelines.

Tensions are high between the US and Russia. The former Cold War foes have a common adversary in Islamic State militants, but have been deadlocked over how to end the war in Syria, with Russia supporting Bashar al-Assad and the US saying he has to step aside.

“In Syria, the combatants are defying all norms of humanity,” UN Secretary-General Ban Ki-moon said ahead of General Assembly sessions.

“Responsibility for ending this horror rests on the parties, and on the neighbours and external forces that are fuelling the fighting.”

More than 250,000 people have been killed in Syria since a 2011 government crackdown on pro-democracy protesters spiralled into civil war, triggering the rise of Islamic State.

Some 7.6 million people have been displaced, while another 4 million have fled. Tens of thousands are now making their way to Europe.

Amid an uproar over the treatment of refugees and migrants by some European countries, Mr Ban has urged European leaders to show compassion.

“Brutal conflicts, breakdowns in basic governance, economic despair and other factors have generated displacements of people not seen since the Second World War,” said Mr Ban, adding that on a global level, a massive 60 million people have fled their homes.

Iranian President Hassan Rouhani and his Foreign Minister, Mohammad Javad Zarif, will also be in attendance.

Mr Zarif is expected to take part in a meeting on Monday with the foreign ministers of the six powers who negotiated a historic nuclear deal with Tehran, including United States Secretary of State John Kerry. Reuters