BRUSSELS- The United Nations urged international donors to pledge up to $10 billion on Tuesday to help Syrians fleeing a decade of civil war in the midst of the COVID-19 pandemic, saying that the need for humanitarian support has never been so great.

In the fifth annual conference to keep Syrians refugees from starvation, the event hosted by the European Union will seek $4.2 billion for people inside Syria and $5.8 billion for refugees and their hosts in the Middle East.

Some 24 million people need basic aid, a rise of four million over the past year and the highest number yet since a crackdown on pro-democracy protesters by Syrian President Bashar al-Assad in 2011 led to civil war.

"I call on you to help us address rising needs and to step up your financial and humanitarian commitments," United Nations Secretary-General Antonio Guterres said in a video message.

"Syria's economy has been ravaged and now the impacts of COVID-19 have made things worse. Almost half of all families lost their source of income. Nine in ten Syrians is living in poverty," he said.

Sweden was one of the first donors to pledge increased support at a time when countries around the world have less money to donate as COVID-19 devastates their economies.

U.S. Secretary of State Antony Blinken late on Monday called for Syria's borders to be kept open to allow unhindered access and the free flow of aid.

Fighting between Syrian army forces and rebels has subsided since a deal a year ago ended a Russian-led bombing campaign that had displaced over a million people, but Russian air strikes, along with Iranian and Syrian-backed militaries, continue to attack rebel outposts.

In a separate statement, the Red Cross Red Crescent Movement urged international donors to help rebuild Syria, particularly to repair critical health, water and electricity services.

"Our infrastructure is ruined," said Khaled Hboubati, the Syrian Arab Red Crescent Society.

Rebuilding destroyed cities will take billions of dollars more and cannot start until powers involved in the conflict, including Russia, Turkey and Iran, help agree a peace settlement, the European Union says.

International Committee of the Red Cross head Peter Maurer urged world powers to reach a peace deal or face many more annual donor conferences for Syria. "Humanitarians are here to help but the ultimate responsibility lies with parties to the conflict," he said.

(Additional reporting by Stephanie Nebehay in Geneva, Editing by William Maclean) ((robin.emmott@thomsonreuters.com; +32 2 287 6835; Reuters Messaging: robin.emmott.thomsonreuters.com@reuters.net))