GENEVA (Reuters) - More than 1.5 million people have fled Syria as conditions there deteriorate rapidly, the United Nations refugee agency (UNHCR) said on Friday.

The exodus has accelerated over the past four months and the agency estimates that nearly 1 million refugees have registered since January, U.N. officials said.

"The fact that more than 1.5 million have registered or have appointments with UNHCR sadly means the actual number is much higher," UNHCR said in a statement, without giving an estimate for the total.

"Refugees tell us the increased fighting and changing of control of towns and villages, in particular in conflict areas, results in more and more civilians deciding to leave," it said.

Most of the refugees have fled to neighboring Lebanon and Jordan where UNHCR said it had counted 470,457 and 473,587 respectively this week.

Syria's population is 23 million.

(Reporting by Emma Farge; Editing by Louise Ireland)