VAN, TURKEY (REUTERS) - Afghans who manage to make the weeks-long journey through Iran on foot to the Turkish border face a 3m-high wall, ditches or barbed wire as the Turkish authorities step up efforts to block any refugee influx into the country.

The beefed-up border measures in Turkey, which already hosts nearly four million Syrian refugees and is a staging post for many migrants trying to reach Europe, began as the Taleban started advancing in Afghanistan and took over Kabul last week.

The authorities plan to add another 64km by the end of the year to a border wall started in 2017. Ditches, wire and round-the-clock security patrols will cover the rest of the 560km frontier.

"We want to show the whole world that our borders are unpassable," Mr Mehmet Emin Bilmez, governor of the eastern border province of Van, told Reuters at the weekend. "Our biggest hope is that there is no migrant wave from Afghanistan."

Turkey is not the only country putting up barriers. Its neighbour Greece has just completed a 40km fence and surveillance system to keep out migrants who still manage to enter Turkey and try to reach the European Union.

The authorities say there are 182,000 registered Afghan migrants in Turkey and up to an estimated 120,000 unregistered ones.

President Tayyip Erdogan urged European countries to take responsibility for any new influx, warning that Turkey had no intention of becoming "Europe's migrant storage unit".

The number of irregular Afghan migrants detained in Turkey so far this year is less than a fifth of the number detained in 2019, and officials say they have not yet seen signs of a major surge since last week's Taleban victory, though the long distances mean refugees could take weeks to arrive.

The Turkish side of the mountainous border with Iran is lined by bases and watchtowers.

Patrol cars monitor round the clock for movement on the Iranian side, from where migrants, smugglers and Kurdish militants frequently try to cross into Turkey.

Migrants who are spotted getting through at the border are returned to the Iranian side, though most return and try again, according to security forces.

"No matter how many high-level measures you take, there may be those who evade them from time to time," Mr Bilmez said.

'Let us stay'

Roads leading from the border are lined with checkpoints. Migrants who make it through are hidden by smugglers in houses - often dirty, ramshackle buildings underground or in deep dried riverbeds - waiting to be moved to western Turkey.

Last Saturday, police captured 25 migrants, mostly Afghans, behind a dilapidated building in Van's Hacibekir neighbourhood.

"We thought we will have facilities here; we will earn to support our parents. There, there are Taleban to kill us," said 20-year-old Zaynullah, one of those detained. He said he arrived in Turkey two days earlier after travelling on foot for 80 days.

Those captured are taken for health and security checks at a processing centre.

There, Mr Seyyed Fahim Mousavi, 26, said he fled his home in Kabul a month ago, before the Taleban came, fearing the militants would kill him because he had worked as a driver for the Americans and Turks.

His wife Morsal, 22, said they took the journey through Iran mostly on foot to escape the Taleban.

"They harm women. After raping them, they kill them. They behead the men," she said, holding her two children, aged two and five. "We don't want to go back. Just let us stay here."

After processing, migrants are taken to a repatriation centre, where they can spend up to 12 months before being sent back to their home country.

Those repatriations have been halted for Afghans now, leaving around 7,500 Afghans in limbo in various repatriation centres.

Mr Ramazan Secilmis, deputy head of the migration directorate, said his organisation was working to identify those who need protection from the Taleban to relocate them to third countries.

"Those who need protection need to be separated from those who come to our country due to economic reasons. We cannot deport anyone automatically just because they have Afghan nationality," he said.