Somali pirates have seized three ships off the coast of the Horn of Africa, after Monday's hijacking of the Sirius Star, a vessel carrying $100m worth of oil.
A Greek tanker, a Thai fishing boat and a Hong Kong-registered vessel have been captured in the past 48 hours despite a large international naval presence in the waters off Somalia.
Andrew Mwangura, co-ordinator of the East African Seafarers' Assistance Programme said on Wednesday that the Greek vessel had been taken in the Gulf of Aden on Tuesday.
According to the International Maritime Bureau (IMB), the Thai fishing boat had 16 crew members on board.
An Indian warship deployed to Gulf of Aden has been engaged in a battle with Somali pirates, the navy has said.
The pirates' vessel had been destroyed, and two accompanying speed boats sped away after the main vessel was blown up.
Piracy 'out of control'
With eight ships being hijacked in the past two weeks, the IMB's piracy reporting centre has described the situation as "spiralling out of control".
Noel Choong, head of the centre based in Kuala Lumpur, Malaysia, said the pirate attacks are becoming "more violent, frequent and extending further from the attackers' bases".
The seizure of the Sirius Star, a Saudi-owned supertanker, on Monday has prompted South Korea to look at sending military vessels to join US, French and Russian warships already operating in the area.
The Sirius Star is the biggest vessel ever hijacked, and Al Jazeera has learned that negotiations have begun on a ransom demanded by the pirates.
The ship is reportedly anchored off the Somali coast at Haradheere, roughly in the centre of Somalia's coastline.
Matthew Oakely, a maritime security consultant, told Al Jazeera that security efforts may be stepped up to protect ships.
"The rules of engagement are now that the military may, if necessary, open fire on suspected pirate ships in international waters, as there was not any order to do this before," he said.
"I am not advocating that you blow people out of the water unless you can be as sure as possible that they are indeed pirates. But I think it may make a difference in due course if examples are made to these people of what the consequences are going to be if they continue with this reprehensible behaviour."
| Pirates have anchored the Sirius Star off the coast of Somalia [AFP]
At least 13 vessels with more than 270 crew members are already being held by various pirate gangs. A Ukrainian-registered cargo ship carrying tanks and heavy weaponry remains anchored off the Somali coast.
Mwangura at the East African Seafarers' Assistance Programme said: "The pirates are sending out a message to the world that 'we can do what we want, we can think the unthinkable, do the unexpected'."
Choong of the IMB reported a spike in attacks, saying: "What we have seen in these last few weeks is an abnormal increase in violence and ships being hijacked despite the increased security in the area.
"The situation is already out of control. The United Nations and the international community must find ways to stop this menace.
"With no strong deterrent, low risk to the pirates and high returns, the attacks will continue."
The Norwegian shipping group Odfjell has already ordered its more than 90 tankers to sail around the cape of Good Hope to avoid attacks.
Terge Storeng, the chief executive officer of Odfjell, told Al Jazeera: "We took this decision to avoid exposing our crew members to risk on their way through the Suez canal.
"We have two to three ships in this area every week. We have already had one attempt of hijacking, so we have been continuously evaluating the risk.
"Of course, this is a huge step for our company to re-route our ship to go all the way around Africa ... But for a chemical tanker to have armed people on board and the risk of a gunfight - its not a good idea."
Last week, the European Union, in its first-ever naval mission, launched a security operation off the coast of Somalia to combat piracy and protect ships carrying aid agency deliveries.
The South Korean military will now seek parliamentary approval to send naval vessels to waters off Somalia to protect the country's commercial fleet, government officials have said.
Somali pirates had recently captured a cargo vessel and held hostage South Korean sailors who were part of the crew of a Japanese ship.