Nairobi - Undaunted Somali pirates have seized a total of four ships - among them two cargo ships - just days after US and French forces killed five pirates in two separate operations to free hostages, officials said Tuesday.

The EU Maritime Centre said that the 35,000-ton MV Irene E.M. was taken overnight, but that the Greek vessel's 22 crew members, reportedly entirely Filipino, were unhurt.

Greece's merchant marine ministry said the Saint-Vincent-flagged vessel was sailing from Jordan to India. It belongs to Piraeus-based shipping company Chian Spirit Maritime Enterprises.

Other reports said that the 5,000-tonne, Lebanese-owned MV Sea Horse, flying a Togo flag, was successfully boarded by pirates, also overnight.

Egypt's foreign ministry said that up to 24 Egyptians had been taken hostage in two separate seizures of fishing boats in the Gulf of Aden on Monday.

Pirates activity has picked up in recent weeks after a lull in activity due to bad weather.

Over 20 ships have been attacked in the last three weeks. Nine of those ships are in pirate hands, bringing the total number of ships being held to 17.

Almost 300 crew members are being held hostage.

The highest profile attack in recent months came last Wednesday, when the US crew of the Maersk Alabama fought off pirates who boarded the ship.

Richard Phillips, the captain of the Alabama, was held hostage on a lifeboat for five days until Sunday, when five US Navy snipers killed the three pirates holding him. A fourth pirate surrendered.

An official for Maersk Line, Limited, the US company that operates the Alabama, said Tuesday that Phillips would be reunited with his crew on Wednesday in the Kenyan port of Mombasa, where the Alabama docked on Saturday.

Phillips has been on the USS Boxer being debriefed and recovering from his abduction.

US President Barack Obama, who authorized the use of deadly force to free Phillips, has vowed to fight piracy off Somalia.

"I want to be very clear that we are resolved to halt the rise of piracy in that region," he said after Phillips was freed. "And we have to ensure that those who commit acts of piracy are held accountable for their crimes."

On Friday, the captain of a French yacht and two pirates died when French naval forces stormed the boat, freeing four hostages.

However, piracy experts have said they do not expect the attacks to deter pirates from seeking multi-million-dollar ransoms.

"We are hoping this (the attacks) will discourage others, but at this stage I very much doubt it," Noel Choong, head of the International Maritime Bureau's Piracy Reporting Centre, told German Press Agency dpa. "There are a lot of pirates out there."

On the contrary, there are now fears that pirates will take more extreme action, increasing the chance of further hostage deaths.

Pirate gangs have already vowed to avenge their dead colleagues by targeting US and French citizens.

In 2008, pirates seized more than 40 vessels in and around the Gulf of Aden and collected tens of millions of dollars in ransoms, prompting the international community to send warships to the region.

Around 15 warships from the European Union, a US-led coalition task force and individual countries such as Russia, India and China patrol an area of about 2.85 million square kilometres.

The presence of the warships has appeared to have had little effect, and observers say that only by tackling insecurity and poverty in Somalia will piracy finally be halted.

Somalia has been without a functioning government since the 1991 ouster of dictator Mohamed Siad Barre.