The number of irregular migrants who crossed into the European Union last year was "just short of 200,000" – the highest number since 2017 – the EU's border agency Frontex said Tuesday.

The number of detected crossings was 57% higher than 2020 when COVID-19 restrictions drastically reduced migration but also 36% higher than 2019, Frontex said in a statement.

The statement said arrivals were now "above pre-pandemic levels."

"This suggests that factors other than the lifting of restrictions on global mobility are the cause of increased migratory pressure," the Warsaw-based agency said.

It said one new factor in 2021 was the influx of migrants – mostly from the Middle East – through Belarus in what the EU says was a deliberate operation by the Belarusian regime.

There were also sharp increases in migrant arrivals through the central Mediterranean, the western Balkans and the island of Cyprus.

The main route was the central Mediterranean – accounting for 65,362 arrivals, or around a third of the total.

The year-over-year increase was 83%, Frontex said.

The western Balkans saw a 124% increase from 2020 to 60,540 people. In Cyprus, there were 10,400 recorded arrivals – 123% higher than the previous year.

Overall in 2021, Syrians mainly comprised the irregular migrants, followed by Tunisians, Moroccans, Algerians and Afghans.