More than 700,000 Syrian refugees have registered in neighbouring countries or await processing there, and aid workers are struggling to keep up with the exodus, the United Nations said on Tuesday.

"We have seen an unrelenting flow of refugees across all borders. We are running double shifts to register people," Sybella Wilkes, spokeswoman for the UN High Commissioner for Refugees (UNHCR), told Reuters in Geneva.

Jordan hosts 167,444 registered Syrian refugees, as well as 51,729 who await processing, many of who fled fighting around Deraa, according to UNHCR figures posted overnight that show an overall regional total of about 705,000 refugees as of Jan. 27.

"We are trying to clear a backlog of people because the numbers have gone up so dramatically (in Jordan and Lebanon)," Wilkes said.

Lebanon has 157,139 Syrian refugees, as well as nearly 69,000 who await processing. "The needs are enormous, we can't get to everyone fast enough," Wilkes quoted Ninette Kelley, UNHCR representative in Lebanon, as saying on Tuesday.

Turkey has 163,161 Syrian refugees in its 15 camps while Iraq hosts 77,415. There are 14,312 in Egypt and 5,417 registered across the rest of North Africa, the agency said.