The head of the European Union's border agency says it is boosting its operations in the Mediterranean near Greece as increasing numbers of migrants try to enter the EU from Turkey.

Frontex Executive Director Fabrice Leggeri told The Associated Press Thursday: "We are worried about the situation in Greece and that's why we will upgrade our action there and our support to the Greek authorities."

More than 10,000 people have been plucked from the central Mediterranean in recent weeks attempting to enter Europe from Libya in overcrowded and unseaworthy boats. Some 1,700 are feared dead.

"There is a shift from the central Mediterranean to the eastern Mediterranean" as more migrants leave Turkey by sea and land, Leggeri said.

"They are moving very quickly so we have to be flexible."