The United States on Thursday announced $535 million in new aid for Syrians, pledging to keep up humanitarian assistance even after fighting in the brutal war has ended.

Uzra Zeya, the US under secretary in charge of civilian security, announced the new funding on the sidelines of the UN General Assembly.

The funding will go through humanitarian groups to assist Syrians including refugees by providing shelter, food, education and healthcare, the US Agency for International Development said.

"While only a negotiated political solution can fully end the suffering of the Syrian people, humanitarian assistance is vital to keeping civilians alive," USAID said in a statement.

"We urge other donors to join us in stepping up to fill the significant funding gaps and ensure partners can continue to meet the needs of the most vulnerable."

Syrian President Bashar al-Assad crushed an uprising that erupted in 2011 in a conflict that killed more than half a million people, displaced seven million more and saw the rise of the ultra-violent Islamic State group.

Assad has largely reasserted control of the country and Arab leaders have increasingly welcomed him back into the fold.

The United States has vowed never to accept Assad without accountability for atrocities during the war.

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