In this photo released by the Italian Navy on Thursday, March 20, 2014, migrants stand on a boat after being rescued along the Mediterranean Sea. Italian Navy/AP

Italian authorities say they have rescued more than 4,000 migrants at sea over the past four days as the war in Syria and instability in Libya spawn new waves of refugees.

The numbers of migrants reaching Italian shores generally rises this time of year as warm weather and calm seas make the Mediterranean Sea crossing from North Africa easier. But the U.N. refugee agency said the numbers so far in 2014 represent a 300 percent increase over the same period in 2013.

Italian maritime officials said 2,922 people were picked up March 17-18, and another 1,165 were rescued Wednesday and Thursday.

Italy has struggled for decades with a steady stream of migrants travelling in small, unsafe boats from North Africa to the tiny island of Lampedusa, midway between Tunisia and Sicily. But the problem has ballooned since the "Arab Spring" turmoil of 2011, the breakdown of order in Libya and civil war in Syria.

"They cannot stay safe in Libya," said Carlotta Sami, spokeswoman for the U.N. refugee agency in Italy, adding that the recent arrivals in Sicily included two Syrian women in their 80s. "Everybody is trying to escape Syria."

Italy beefed up its air and sea surveillance of the sea smuggling route after two incidents off the coast of Lampedusa last year in which hundreds of migrants drowned.

Nearly 43,000 migrants arrived by sea in Italy in 2013.

Wire services