"We have signed a contract on behalf of the Qatari navy to acquire seven warships from Italy for five billion euros ($5.9 billion)," Foreign Minister Sheikh Mohammed bin Abdulrahman Al-Thani said at a Doha press conference with his visiting Italian counterpart Angelino Alfano.
It follows the signing of a preliminary contract in June 2016 for the deal between the Italian group Fincantieri and Qatar for four corvettes, an amphibious vessel and two patrol boats.
In June this year, the United States agreed a $12-billion sale of F-15 fighter jets to Qatar, re-affirming support for the emirate in the throes of the worst diplomatic crisis to hit the Gulf in decades.
Saudi Arabia and its allies including Egypt and the United Arab Emirates cut diplomatic and trade ties with Qatar on June 5, accusing Doha of backing extremist groups and being too close to Riyadh's arch-rival Iran.
Qatar denies the allegations and accuses the Saudi-led bloc of imposing a "siege" on the tiny emirate.
Alfano called for a de-escalation and a solution that shows "respect for international law".
The Saudi-led bloc has demanded that Qatar close regional news giant Al-Jazeera and a Turkish military base, and downgrade its ties with Iran.
Doha has dismissed the demands as a violation of its sovereignty.