The speaker of Poland's upper house of parliament has called on the government to reveal what it knew about an escalating cash-for-visas scandal.

Tomasz Grodzki said the issue was ruining the country's international reputation as a responsible democracy.

The government has released few details but media reports say migrants paid up to $5,000 (£4,000) each to speed up their work visa applications.

Seven people have been charged so far but none are public officials.

The country's Deputy Foreign Minister Piotr Wawrzyk was sacked last week following the allegations.

His dismissal came the same day that Poland's Anti-Corruption Bureau (CBA) carried out a search of the foreign ministry. The director of its legal service has also been fired.

The ministry, which is facing an audit in relation to the scandal, said it would terminate all contracts for outsourcing companies handling visa applications since 2011.

Opposition MPs said up to 250,000 visas for people from Asia and Africa were issued irregularly by outsourcing companies.

The government disagreed with this figure, saying only several hundred were issued.

"Anyone who wants to get from Africa to Poland goes to our embassy, ​​buys a stamped visa at a special stand, fills in their details and off they go! PiS [governing party] migration policy," wrote Donald Tusk, the leader of the opposition Civic Platform party, on X (formerly Twitter).

Prime Minister Mateusz Morawiecki has accused Mr Tusk of trying to stir up problems for his governing Law and Justice party (PiS) and denied that there is a widespread issue.

"This case is ruining our country's reputation as a responsible member of the democratic community of the free world and jeopardizes our security, therefore it must be explained in detail," said Mr Grodzki, speaker of Poland's upper house, in a televised address on Friday.

"This is the biggest scandal we have faced in the 21st century. Corruption at the highest levels of government, bringing a direct threat to all of us."

Justice Minister Zbigniew Ziobro later said in an interview with state-run news channel TVP Info that Mr Grodzki was exaggerating the scale of the problem.

The CBA said it first became aware of the matter in July 2022 and has been working to verify it since.

The scandal threatens to tarnish the PiS's anti-immigration stance ahead of parliamentary elections that are due in a month's time.

PiS is seeking an unprecedented third term in office and while they are currently leading in polls, it is unclear if they can win the outright majority they need to govern.