Italian officials say good weather is the main factor behind a spike in migrant crossings from Libya, with mostly Italian ships picking up 3,100 migrants over the last three days.

Coast Guard Cmdr. Filippo Marini said Thursday that "in these days there has been a window of weather that has been good for transiting this section of sea."

The U.N. refugee agency says 9,800 migrants arrived in Italy this year through Wednesday, compared with 7,400 in the same period last year. Spokeswoman Barbara Molinario said that it was too early to speak of trends and this kind of concentration in short periods is not unprecedented.

The International Organization for Migration says other factors beyond weather may be at play, such as the availability of boats in Libya.