At least 21 refugees have drowned off Turkey after their boats overturned in rough waters in two separate incidents as they tried to reach the Greek island of Lesbos, authorities said.

Nine bodies washed up on a beach in the resort town of Ayvalik early on Tuesday morning, prompting authorities to dispatch coast guard boats and gendarmerie officials to search the area by sea and by land for possible survivors. By late morning, the death toll reached 14, the coast guard said, adding that seven other migrants were either rescued or found alive.

Hours later, the private Dogan news agency reported that seven other bodies had washed up on shore at Dikili, a resort about 30 miles south of Ayvalik, the victims of a second migrant tragedy. The dead included women and children, the agency said.

Around 850,000 migrants and refugees crossed into Greece last year, paying smuggling gangs to ferry them over from Turkey in frail boats. Hundreds have lost their lives during the crossings.

The International Organisation for Migration (IOM) estimates that 3,771 migrants overall have died while trying to cross the Mediterranean Sea to Europe last year. The final number for 2015, released on Tuesday, was up from the 3,692 figure the agency released before Christmas.

The IOM said last year was the deadliest on record for migrants crossing the Mediterranean, with the number of deaths rising from 3,279 in 2014. The IOM said a large majority of the deaths last year were still on the central Mediterranean route, mainly involving people crossing from Libya - 2,892, or 77%. However, there were 805 deaths in the eastern Mediterranean -accounting for 21% of the total, up from only 1% the previous year - as that route became more popular.

Top officials from Denmark, Sweden and Germany, meanwhile, were scheduled to hold talks in Brussels on Wednesday amid concern about new border control measures aimed at stopping migrants entering northern Europe, EU officials said.

Sweden introduced ID checks on all people traveling to Denmark, and Denmark tightened border controls on its border with Germany on Monday for at least 10 days, citing concerns about public security because of migrant movements and border measures taken by other EU member states.

Danish officials said 18 people without proper ID were refused entry from Germany in the first 12 hours of the increased border crossing checks. Three people were also arrested, suspected of human smuggling.

In Turkey, Namik Kemal Nazli, the local administrator for Ayvalik, told the state-run Anadolu Agency that the victims of the first incident are believed to be from Iraq, Algeria and Syria. There was no information on the nationalities of those drowned in the second incident.

A body with a lifejacket was pulled from the sea on to the beach at Ayvalik by a fisherman and a military police official, Dogan news agency video footage showed. Other bodies, also in lifejackets, were seen lying nearby.