(Reuters) - An Iranian-flagged cargo ship has fled from waters around Sri Lanka after weeks of detention by the island nation's navy acting on a court order obtained by Germany's DVB Bank SE, officials and a lawyer acting for the bank said on Thursday.

The Sri Lankan navy last week fired warning shots to prevent the MV Amina from leaving, but said that late on Wednesday the vessel made its way in rough sea out of the country's waters.

"If the ship is beyond 12 nautical miles from our shores, then we can't do anything according to U.N. laws unless the ship has committed any crimes in our country," Sri Lankan Navy spokesman Kosala Warnakulasuriya said.

"We tried to communicate and asked her to stop, but without responding to anything, she had gone."

The vessel is managed by Tehran-based Rahbaran Omid Darya Ship Management, public shipping registers and ship tracking data showed. The European Union and United States have said the firm is a front for the Islamic Republic of Iran Shipping Lines (IRISL), which has faced Western sanctions for some years.

The West has accused IRISL, Iran's biggest cargo carrier, of transporting weapons, a charge it denies.

IRISL officials told Reuters the ship was owned by a private company and could not discuss the matter. Rahbaran Omid Darya Ship Management could not be immediately reached for comment.

The MV Amina was seized in December after DVB Bank obtained an order on December 12 from the Colombo High Court to hold the vessel after the owners defaulted on a payment. Court documents showed that DVB Bank sought to recover millions of dollars.

A DVB Bank spokesman did not immediately comment on the issue.

"It has broken arrest and now it's a rogue ship and it has gone to Indian waters," said a lawyer for Neelakandan & Neelakandan, a Colombo-based legal firm acting for DVB Bank, declining to be named.

It was not possible to immediately confirm the exact location of the ship. Tracking data last shows it sailing away from Sri Lanka into the Laccadive Sea, a waterway bordering India.

"We have alerted the nearest coast guard vessel. Effort to track is on," Jacob Thomas, director of ports in the state of Kerala, told Reuters when asked if the MV Amina was in waters off the Keralan coast.

An arrest occurs when a ship is detained by a court order to secure a maritime claim. The arrest may ultimately result in a judicial sale of the ship to pay the claim.

IRISL has tried to dodge sanctions by changing its flags and setting up front companies, the U.S. Treasury and the European Union have said. Last year IRISL Managing Director Mohammad Hussein Dajmar said if pressure from Western sanctions continued the group would face increasingly grave problems.

Sri Lankan officials said there were 24 crew members on the ship, including eight Indians who were returned to their home country after the arrest. Iranian crew members were left aboard and a shipping agent provided them with food and other supplies.

According to the Times of India newspaper the ship had set sail from China on November 18 and reached Sri Lankan waters on December 6. It was not clear what cargo it was carrying.