Turkish hackers targeted the former European Parliament rapporteur on Turkey last week, apparently in retaliation for the politician's criticism of the country's rights record.
The websites of both MEP Kati Piri and the Dutch Labour Party, of which Piri is a member, were rendered inaccessible for several hours on Saturday afternoon.
The Turkish hacker group Anka Neferler Tim claimed responsibility for the attack, Duvar reported.
"We have closed the website of the Dutch politician Kati Piri and the Workers Party, of which she is a member. Know your place!" the group said in a tweet.
Piri previously served as the European Parliament's rapporteur on Turkey.
The Dutch politician routinely drew Turkish ire for her criticism of President Recep Tayyip Erdogan and alleged rights abuses by his government.
Despite leaving the role in 2019, Piri has continued to comment on Turkish affairs. Most recently she appeared at an Amsterdam rally in support of Turkish student protesters.
"It appears that this is an attack following my support for Democrats in Turkey and my call for the release of political prisoners such as Selahattin Demirtas and Osman Kavala," she said in a tweet.
European lawmakers and bodies including the European Court for Human Rights have urged the release of both Demirtas, a pro-Kurdish politician jailed on terror charges, and Kavala, a philanthropist and civil society figure accused of attempting to overthrow the Turkish government.
The court found their detentions to be in violation of their rights, a ruling Ankara has rejected.
Piri earlier this month led a call urging member states of the Council of Europe to push for Demirtas' release.
The effort was met with a fierce rebuke by Turkish Interior Minister Suleyman Soylu.
"You'll grow old with these ugly requests," Soylu said in a tweet directed at Piri. "They will never come about in Turkey."
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