Five of the seven Somali pirates who are sentenced to a jail term of 20 years each sit in court at the Kenyan coastal town of Mombasa August 8, 2012. The pirates have been found guilty of hijacking a fishing vessel trawler named Captain St. Vincent while armed with offensive weapons on October 27, 2009, in the international waters off the Gulf of Aden within the Indian Ocean, according to prosecution documents presented in court. REUTERS/Joseph Okanga NAIROBI (Reuters) - Pirates have seized a merchant ship in the Red Sea and have taken it south towards Somali waters in the first successful hijacking in the region since 2012, maritime officials said on Sunday.

The vessel, identified as the MV Marzooqah, sent a distress signal on Saturday evening in the Red Sea and was then turned towards the Gulf of Aden, Andrew Mwangura, secretary general of the Seafarers Union of Kenya, told Reuters.

The number of attacks by Somali pirates dropped sharply in 2013, largely because of an international naval effort. But maritime experts have said the problem will remain as long as gangs operating out of Somalia are not disbanded on land.

Relative stability in Somalia in the past two years after 20 years of chaos and war has raised hopes that it could lead to a more permanent solution to a problem that has driven up shipping insurance rates, but it has yet to solve the issue.

"Now we are trying to follow this ship to try to find out ... which pirate group is holding them and what are their demands," said Mwangura, based in the Kenyan port city of Mombasa.

He said the vessel was crewed by Indians, Egyptians and Syrians and boarded by a gang of eight or nine pirates, and that about five gunmen were still on board. The ship had also been attacked in 2011, but had escaped that time, he said.

Mwangura did not say how may crew were on the ship.

The European Union Naval Force Somalia (EU NAVFOR) said it had information that a merchant vessel had been attacked in the Red Sea, beyond its area of operation which lies further south, and that the ship was now under the control of the hijackers.

Lieutenant Commander Jacqueline Sherriff, a EU NAVFOR spokeswoman based in London, said the force would be using its maritime patrol aircraft to investigate its operational area and would use its naval assets should the ship enter that region.

She said also said that because the attack appeared to have happened in Eritrean waters it was not classified as piracy under international law. Hijackings on the high seas are considered piracy, while inside territorial waters such attacks are considered a maritime crime.

The EU NAVFOR region of operations includes the southern tip of the Red Sea, the Gulf of Aden and Indian Ocean areas.

According to the website vesselfinder.com, the Togolese flagged MV Marzooqah, built in 1978, is 2,196 deadweight tonnes and its last listed port call was on Tuesday in Jeddah, the Saudi Arabian Red Sea port city.

There were 176 confirmed piracy attacks in the region in 2011 and 36 in 2012. Sherriff said the number fell to seven in 2013 and no ships were successfully seized. But she said the naval force had long warned sailors that the threat remained.

"Because the conditions in Somalia have not changed significantly or to any great extent ... we have been saying there is no room for complacency," she said.

(Additional reporting by Richard Lough; Writing by Edmund Blair; Editing by Pravin Char)