Qatar accused the United Arab Emirates on Monday of violating international law after reports suggested Abu Dhabi orchestrated the hacking of the Qatari official news agency and social media sites.
"The information published in the Washington Post ... revealed the involvement of the United Arab Emirates (UAE) and senior Emirati officials in the hacking of Qatar News Agency," Qatar's government communication office said in a statement on Monday.
The report "unequivocally proves that this hacking crime took place", the statement quoted Sheikh Saif bin Ahmed Al Thani, director of the government communication office, as saying.
"This criminal act represents a clear violation and breach of international law and of the bilateral and collective agreements signed between the member states of the Gulf Cooperation Council, as well as collective agreements with the Arab League, the Organisation of Islamic Cooperation, and the United Nations."
The statement said that an investigation is ongoing and that government prosecutors plan to take "legal measures" locally and abroad.
The Washington Post reported on Sunday that the UAE helped arrange the hacking.
However, UAE's minister of state for foreign affairs Anwar Gargash said the latest report "is simply not true" and denied his country's role in the incident.
The Washington Post reported that US intelligence officials learned last week of newly analysed information that showed that senior UAE government officials discussed the planned hacking on May 23, the day before it occurred.
The officials said it was unclear if the UAE hacked the websites or paid for it to be carried out, the newspaper reported.
The report did not identify the intelligence officials it spoke to for the report.
In an interview with Al Jazeera, Mohammed Cherkaoui, professor on conflict resolution at George Mason University, said the new Washington Post "bombshell" shows that the Gulf crisis "is moving from one escalation to another".
"I am still wondering how we can curb this trend of escalation, and how we can restore some positive perceptions between the stakeholders, as well as some dialogue," Cherkaoui said.
"So far, we have several setbacks of regional and international mediation."
Martin Reardon, an intelligence expert and an FBI veteran, said that while the UAE is "not sophisticated enough" to carry out the hacking on its own, there are hackers "available for contracting".
The controversy started on May 23, when alleged hackers reportedly posted fake remarks on Qatar's official media platform criticising US foreign policy and attributing the statement to the country's emir.
In the articles, Qatar's Emir Tamim bin Hamad Al Thani was quoted as cautioning against confrontation with Iran, as well as defending the Palestinian group Hamas and Hezbollah, a Lebanese Shia movement allied with Tehran.
Qatar's government categorically denied that the comments were ever made and claimed that its websites were hacked. It also asked the US Federal Bureau of Investigation to help in the probe.
But following the publication of the stories, Saudi Arabia and the UAE blocked Qatar-based websites including Al Jazeera, and later led a group of countries in cutting diplomatic ties with Doha.
Meanwhile, Daniel Hannan, a conservative British member of the European Parliament, said the continuing blockade on Qatar is not helpful in resolving the crisis.
"There is almost no situation in the world that isn't made worse by an economic blockade," Hannan told Al Jazeera.
"This pain is felt by all sides," he said. "We are looking to have a speedy and serious de-escalation of the situation, and a solution that respects press freedom and national sovereignty."
Hannan said an "immediate lifting" of the sanctions could pave the way for talks, saying "it is very difficult to negotiate with a gun to your head."