GENEVA May 3 (Reuters) - An estimated 113 people died in four shipwrecks between Libya and Italy at the weekend as the crossing becomes the preferred sea route for migrants to Europe, the International Organization for Migration (IOM) said on Tuesday.

With the closing of land routes in the Balkans and a recent deal under which Greece sends migrants back to Turkey, Italian officials have said they expect more people to try to make this longer and much more dangerous crossing from Libya.

In one of four incidents, an Italian merchant ship rescued 26 people off the coast of Libya in rough seas and others were feared missing, Italy's Coast Guard said on Saturday.

IOM, citing survivor testimony, said 84 people appeared to be missing from that wreck, while at least 29 drowned in two other attempted crossings in rubber dinghies of the Channel of Sicily. It was still investigating a fourth incident.

"Just since Friday we know of 4 shipwrecks and 113 people killed, just off Libya," IOM spokesman Joel Millman said.

"It is becoming the preferred route. So therefore we are very mindful of what could be coming in the next few months," Millman told a news briefing.

Migrants from West Africa, especially Nigerians, and the Horn of Africa dominate the Libya-Italy route, which Syrians, Afghans and Iraqis are not taking for now, Millman added.

In all, 1,357 migrants and refugees perished at sea during the first four months of the year, mostly along the Central Mediterranean route, against 1,733 during the period in 2015, the agency said.

Since January, 28,593 migrants and refugees have arrived by sea in Italy, while 154,862 have landed in Greece, the IOM said. (Reporting by Stephanie Nebehay; Editing by Alexander Smith)