The move follows a decision by Interior Minister Marcin Kierwiński, state news agency PAP reported.
"We are extending border controls to monitor the migration route from the Baltic states through Poland to Western Europe," Kierwiński said on X.
"We have been catching individuals who illegally attempt to smuggle migrants to the West. Maintaining the integrity of the border with Belarus and protecting it from migratory pressure remains a key task for our Border Guard," he added.
Poland reintroduced temporary border checks with Germany and Lithuania on July 7 in an effort to curb what officials described as an uncontrolled influx of migrants.
Initially put in place for 30 days, the measure was subsequently extended until October 4. The latest extension further prolongs the checks by six months.
Under the measures, Polish Border Guard officers, supported by police and soldiers, are authorized to stop and inspect selected vehicles.
The government says the checks are necessary to reduce irregular migration across the country's western and eastern borders.
Polish Prime Minister Donald Tusk said in the summer that the move stemmed from the need to curb uncontrolled migration flows and respond to what he described as asymmetrical actions by neighbouring states.
He told reporters at the time that the decision was prompted by Germany's refusal to accept back migrants trying to reach its territory, a departure from past practice.
"This has led to tensions and a justified sense of asymmetry," the Polish prime minister said.
"Without checks on our side, it’s difficult to verify whether the people being sent back to Poland should be returned at all," he added.
Germany reinstated its own border checks with Poland in October 2023 in an effort to prevent illegal migration.
Tusk insisted that Poland remained committed to the principle of borderless travel within the European Union, "but this must be a shared, symmetrical will among neighbours," he said.
In the case of the border with Lithuania, the reintroduced checks apply not only to official crossings but also so-called "green border" areas such as forests and local roads, according to officials.
These operations are supported by Poland's Territorial Defence Force (WOT) and other military units, and anyone found crossing the Polish-Lithuanian border illegally is returned to Lithuania, reporters were told.
Poland's authorities have called on various EU members to work more closely to disrupt what they described as large-scale people-smuggling operations orchestrated by Russia and Belarus.
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Source: IAR, PAP