Turkey has built a new concrete border wall in an effort to stop an influx of people from Afghanistan from crossing into the country, via Iran.The massive concrete structure-- in the eastern province of Van -- stretches 40 miles long.It comes as the number of Afghan migrants trying to enter the country from Iran has risen.Many are refugees fleeing violence in Afghanistan after the United States and its NATO allies withdraw troops and Taliban fighters seized territory.Emin Bilmez is a local governor: "The number of refugees we seized on borderline and thwarted last year is around 105,000. This year, the number of refugees we seized on border and started legal proceedings with has exceeded 55,000."Afghans have been crossing from Iran into Turkey for years, many of them en route to Europe. But the number of detentions this month has raised concerns about a new influx.Turkish authorities intercepted a boat carrying more than 200 Afghan migrants in the Aegean sea heading for Europe, the coastguard said on Wednesday. Last week officials said they had detained 1,500 irregular migrants, most of them Afghans, near the Iranian border in the past 10 days.President Tayyip Erdogan's government, which is already hosting 3.7 million Syrian refugees says it wants to avoid another refugee wave.The UNHCR said an estimated 270,000 Afghans had been newly displaced inside the country since January.That brings the total population forced from their homes to more than 3.5 million.