“The relevant regulation was issued and sent to the European Commission for notification on Friday,”  Kierwinski said at a meeting with regional governors.

He said the checks, which were introduced last month after Germany imposed similar ones to stop undocumented migrants, would be extended until Oct 4.

Kierwinski said increased checks and barriers on Poland’s border with Russia and Belarus had stopped irregular migrants transiting through those countries.

He added it was now “fundamental” to close the route being used by migrants through the Baltic states of Latvia and Lithuania and then across Poland to Germany.

Polish officials estimate that hundreds of migrants, mainly from the Middle East, are crossing into the Baltic states every month from ex-Soviet Belarus.

EU countries within the free-movement Schengen area are allowed to impose border controls if they feel there is a threat to public order or internal security.

“There is full understanding on the part of our European partners, because… these decisions are intended to close the migration route that has now re-emerged through Lithuania and Latvia,” Kierwinski said.

Border guard chief Robert Bagan said at the same meeting that border guards had checked more than 493,000 people crossing the borders with Germany and Lithuania between July 7 and Aug 2.

He said that during that time border guards had refused entry into Poland to 124 foreigners at the border with Germany and 61 people at the border with Lithuania.

He said 14 people had been detained for aiding illegal immigration in the Lithuanian border area over the same period.