Riga  - Four tugboats freed the cruise ship Mona Lisa in the Baltic Wednesday, three days after it ran aground 17 kilometres off the Latvian shore.

The 201-metre Mona Lisa ran aground Sunday in the Irbe Strait between Latvia and the Estonian island of Saaremaa with almost 1,000 people on board.

The ship was to be towed to the seaport of Ventspils, 37 kilometres from the accident, according to Delfi news website.

More than 650 passengers, mostly elderly Germans, were evacuated Monday and sent home by plane from Riga on Tuesday.

Tugs from Sweden, the Netherlands, and Denmark worked to take the 42-year-old Mona Lisa to deeper waters.

Cause of the accident was "a very big navigational error," Latvian Maritime Administration spokeswoman Sarma Kocane told the Diena newspaper Wednesday.

The ship ran aground because of the error of the crew, a representative of the Lord Nelson Seereisen company told Leta news agency.

According to the company, the ship has sustained minimal damage and could sail back to Germany Saturday. (dpa)