Germany announced Friday it would provide the UN's cash-strapped refugee agency with an extra $135 million in funds to help cope with the massive outpouring of Syrians into neighboring Arab countries.

In a speech before the United Nations General Assembly, Foreign Minister Heiko Maas said it was "shameful" that the UN High Commissioner for Refugees (UNHCR) was running short of cash to aid the millions of Syrians who have fled war in their homeland and called on other wealthy countries to step up to the plate.

"As the second-largest humanitarian donor, Germany is willing to provide UNHCR with a further 116 million euros ($135 million) -- that is half of the amount currently needed -- to help Syrian refugees in Jordan and Lebanon," Maas said.

"But others also need to step up. After all, the Charter talks about 'we the peoples'," he said in reference to the UN's founding treaty.

Syrians accounted for a significant proportion of the hundreds of thousands of migrants that Germany has accepted across its border since 2015 -- an influx which has weakened Chancellor Angela Merkel politically and split the European Union.

With immigration becoming an increasingly toxic issue in Germany, Merkel's government has since repeatedly tightened immigration and asylum laws.

According to the UN, around 5.6 million Syrians are living outside the country as refugees as a result of a devastating seven-year war.

The foreign minister's speech to the body also included several thinly-veiled rebukes to US President Donald Trump's "America First" foreign policy.

The United Nations "thrives on our common pledge of 'together first'," said Maas whose center-left Social Democratic Party is a junior partner in Merkel's coalition.

Speaking of climate change, Maas also criticized governments who put "my country first" as he restated Germany's commitment to the internationally-backed Paris agreement to combat global warming that Trump has decided to quit.