The number of refugees crossing the European Union's external borders was 1.2 million from January to October this year, four times higher than the 282,000 recorded crossings last year, the bloc's border agency reported Tuesday.

The total number of irregular immigrants is lower than that because many people, notably who reach Greece then leave the EU again by crossing into Macedonia and re-cross the EU external border into countries like Hungary, are counted twice.

Frontex said Syrians constitute the largest number of arrivals, but that the number of Afghan nationals has risen in the recent weeks.

More than 150,000 people crossed from Turkey to Greece last month, compared to less than 8,500 crossed in October 2014, Frontex said. Total number arrived in Greek islands was 540,000 in January – October period.

However, the number of people crossing by boat from Libya to Italy was just 8,500 in October, half the level of a year earlier. Some 140,000 have made that crossing so far this year, compared with nearly 155,000 in the same period of 2014.

The border agency has also offered to increase its presence on the Greek land borders with the Former Yugoslav Republic of Macedonia and Albania, as well as Croatia's border with Serbia.

"We are in close contact with Greece and Croatia to fine tune the kind of support these EU Member States expect from Frontex," Frontex Executive Director Fabrice Leggeri said in a statement Tuesday.