Hungary says it has started to roll out barbed wire along its border with Slovenia, after it set up similar barriers along its frontiers with Serbia and Croatia to keep refugees out.
This is the first such known measure to take place in countries belonging to the EU's cherished Schengen passport-free zone, which has already come under intense pressure as states reintroduce border checks to stem the flow of migrants.
"We have started setting up a barbed-wire barrier at the Slovenian border too," said Hungarian government spokesman Csaba Rigo on Thursday (local time), according to state news agency MTI.
Budapest sealed its border with Serbia last week, closing the main crossing after laying down razor wire along the entire frontier, prompting thousands of migrants to divert their route and enter Croatia instead.
It has also laid a razor-wire barrier along 40km of the frontier with Croatia not marked by the Drava river, and announced on Thursday it would decide "soon" whether to in turn close its border with its neighbour.
"The effective protection of Schengen borders can only be ensured with a complete closure," said Janos Lazar, the right-hand man of Hungarian leader Viktor Orban.
The closure of its border with Croatia could divert the flow of refugees further towards Slovenia, as they trek to northern Europe.
In a three-minute story, Hungary's M1 television showed three rows of barbed wire laid out at the Slovenian border over several hundred metres, near the M70 highway that crosses the frontier to the town of Lendava in Slovenia.
It also took shots of mobile iron gates that could potentially be used to close the highway.
Slovenia's foreign ministry told AFP it was aware that Hungary had started laying down a barrier at its border.
"We have been in touch with the Hungarian side and we expect additional information or explanations," it said.