Hackers attacked the websites of one of Portugal's biggest newspapers and of a major broadcaster, both owned by the country's largest media conglomerate Impresa, taking them down over the weekend.

Expresso newspaper and the SIC TV station both said they reported the incident to the criminal investigation police agency PJ and the National Cybersecurity Centre (CNCS) and would file a complaint.

The alleged hackers, calling themselves the Lapsus$ Group, published a message on the websites saying internal data would be leaked if the media group failed to pay a ransom. The message included email and Telegram contact info.

The group did not immediately reply to a Reuters request for comment.

Lapsus$, which claims that it gained access to Impresa's Amazon Web Services account, also sent a phishing email to Expresso subscribers and tweeted from the newspaper's verified Twitter account.

The same group allegedly hacked the Brazilian Health Ministry's website last month, taking several systems down, including one with information about the national immunization program and another used to issue digital vaccination certificates.

CNCS's coordinator, Lino Santos, told Observador newspaper it was the first time the group had launched an attack in the country.

The websites of Expresso and SIC have been offline since Sunday, with the pages showing a message saying they are "temporarily unavailable" following the attack and would return "as soon as possible."

In the meantime, both media organizations are publishing news stories on their social media channels. They described it as an "unprecedented attack on press freedom in the digital age."