MOSCOW -- Poland's prime minister was forced to hastily apologize on Friday after it emerged that his government had apparently unwittingly aided in the arrest of a prominent human rights activist in Belarus by supplying banking information to officials there.

The Polish prosecutor's office confirmed that it had sent details from the Polish bank account of the activist, Ales Belyatsky, as part of a routine information request, despite warnings from the Foreign Ministry to treat such requests with caution.

"I apologize on behalf on the Republic of Poland," Radoslaw Sikorski, Poland's prime minister, wrote on his Twitter account. "A reprehensible mistake despite the Foreign Ministry's warnings. We will redouble efforts to support democracy in Belarus."

The government of Lithuania also passed on similar information to Belarus; it has also apologized.

The revelations were an embarrassment for Poland and Lithuania, both European Union members. They border Belarus, and have been vocal critics of the country's strong-arm president, Aleksandr G. Lukashenko, who has ruled for 17 years.

Mr. Belyatsky, the head of the rights group Vyasna, was jailed last week on charges of evading taxes on funds held in foreign bank accounts, though his supporters deny he did anything wrong.

Amid a continuing crackdown on political dissent in Belarus, Vyasna has been one of the few organizations in a country where independent information is scarce to provide details about the arrests, trials and frequent abuse of Mr. Lukashenko's opponents.

Mr. Belyatsky played a crucial role in lobbying European officials to impose strict economic sanctions on Belarus as well as travel bans for members of Mr. Lukashenko's government this year.

He is one of dozens of political activists who have been arrested over the last year in an apparent effort to quash dissent in the face of an economic crisis.

Mr. Belyatsky's arrest was met with strong condemnation from Western leaders, including those in Poland and Lithuania, whose role in the arrest appeared to take many officials in the two countries by surprise.

Tatyana Revyako, one of Mr. Belyatsky's colleagues, said that Mr. Belyatsky did indeed possess bank accounts in Poland and Lithuania, but that they were not for his personal use, as Belarussian authorities had charged.

Rather, she said, the accounts contained money provided by foreign human rights donors for Vyasna's operations. The organization has been barred from registering in Belarus and is not permitted to open a bank account there.

"It is good they apologized," Ms. Revyako said. "Because it really was a serious mistake."

First Published: August 13, 2011, 4:00 a.m.