A U.S. official says Washington is planning to increase the number of Syrian refugees allowed to resettle in the United States, mostly for vulnerable cases.

Assistant Secretary of State Anne Richard says the numbers will still be very small compared with the nearly 4 million Syrians who have become refugees in neighboring countries, mostly Lebanon, Jordan and Turkey.

Richard told reporters at the U.S. Embassy in Beirut on Thursday that the U.S. has received 648 Syrian refugees since the crisis began in 2011.

She says the U.S. is "moving to bring more refugees to the United States, and that between 1,000 and 2,000 will be brought in by the end of September.

Richard says Washington seeks to bring "those who have severe medial conditions, widows and orphans" and traumatized people.