Yemen has seen a surge of refugees from Somalia and Ethiopia, with a record 12,545 arriving by sea last month as they fled unrest, famine and persecution, the UN refugee agency said on Friday.

The October total -- the highest since UNHCR records began in 2006 -- brings the number of people who arrived in Yemen by boat this year to 84,656, well above the 2009 high of 77,000.

Of the arrivals roughly three quarters were from Ethiopia and the remainder from Somalia.

"We are really experiencing a surge," said Melissa Fleming, spokeswoman for the UN High Commissioner for Refugees.

Somalis said conflict, insecurity, drought and famine were driving them to leave their country, while Ethiopians cited a lack of economic opportunities, with some saying they had fled in fear of persecution in their region.

The UNHCR said it was concerned that most arrive in Yemen unaware of the insecurity and fighting in many parts of the country "which makes further movement difficult and risky."

"We are concerned about an increasing trend of abductions, extortions, kidnappings and sexual assaults targeting refugees, and particularly Ethiopian migrants," a statement said.

Between 2006 and 2008, Somali refugees accounted for the majority of all arrivals in Yemen, but Ethiopian migrants have since constituted the largest group among those crossing the Red Sea and the Gulf of Aden.

The United Nations on Friday downgraded famine declarations in three Somali regions, but warned the crisis remains the worst in the world with nearly 250,000 people facing imminent starvation.

Much of southern Somalia is controlled by Islamist Shebab rebels, who are battling both the Western-backed government in Mogadishu and Kenyan troops in the far south, after Nairobi sent troops across the border last month.