BRUSSELS, Dec 15 (Reuters) - Some 108,000 migrants arrived in Greece in November, roughly half the number recorded the previous month, as worsening weather conditions make crossing the Mediterranean from Turkey even more dangerous, the EU border agency Frontex said.

Greece has been a key point of entry for irregular migrants as the European Union struggles with its worst migration crisis since World War Two. On Tuesday, the bloc rolled out proposals aimed at stemming the influx.

The agency also said a total of 1.55 million irregular border crossings into the EU were registered between January and November. The total number of irregular immigrants is lower, however, as many people are counted twice.

Frontex said some 715,000 people arrived in Greek islands in the first 11 months of the year, 16 times the number in the same period the year before, with Syrians dominating among the group, followed by Afghans and Iraqis.

The agency said the number of people crossing by boat from Libya to Italy fell again last month from October to 3,200 people, bringing the 11-month total to 144,000 via this route, with most arrivals coming from Eritrea and Nigeria. That was 10 percent fewer than in the same period in 2014, it added.

For the Western Balkans route - on which migrants tend to arrive in Greece, exit the EU through Macedonia and re-enter in Hungary or Croatia - Frontex gave the number for November at 164,000, down a fifth from October.

But it said the figure for the January-November period reached nearly 667,000 and marks a 22-fold rise from the first 11 months of 2014. (Reporting by Gabriela Baczynska; Editing by Philip Blenkinsop and Raissa Kasolowsky)