This undated photo shows the Greek-managed bulk carrier MV Irene E.M., which was hijacked by Somalian pirates in the Gulf of Aden during the early hours of Tuesday. (Roberto Smera/Associated Press)

Somalian pirates seized two more ships and reportedly fired on another vessel on Tuesday in the dangerous waters off the Horn of Africa, bringing the total of ships seized to four in the last two days.

The pirates' actions are seen as a brazen response to recent U.S. and French military rescue operations that killed five of their colleagues.

NATO spokeswoman Shona Lowe said the Lebanese-owned MV Sea Horse was attacked Tuesday off Somalia's coast by pirates in three or four speedboats. She had no further details.

Meanwhile, Reuters quoted another NATO official as saying 10 pirates on board three skiffs fired automatic rifles and rocket-propelled grenades at the Liberian-flagged 21,887-tonne Safmarine Asia.

There was no immediate word of any casualties in either incident.

Earlier Tuesday, the Greek-managed bulk carrier MV Irene E.M. was sailing in the Gulf of Aden from the Middle East to South Asia when it was raided, said Noel Choong, who heads the International Maritime Bureau's piracy reporting centre in Kuala Lumpur.

A Canadian warship in the region, HMCS Winnipeg, sent a helicopter to monitor the situation after receiving a distress signal from the vessel, a NATO spokesperson said.

By the time the helicopter arrived on the scene, the MV Irene E.M. was already in control of the pirates, the spokesman said.

The vessel reportedly has as many as 23 crew, whose condition was unknown.

The latest seizure came a day after Egypt's Foreign Ministry said Somalian pirates took control of two Egyptian fishing boats with as many as 24 people on board.

Piracy a 'crisis': rescued crew member

While piracy has been a scourge for years on vessels using shipping lanes off the Somalian coast, the pirates vowed this week to exact their revenge on U.S. and French ships in the dangerous waters after the rescue operations.

On Sunday, U.S. navy SEAL snipers rescued American ship Capt. Richard Phillips on Sunday by killing three young pirates who had been holding him captive in a drifting lifeboat. A fourth pirate surrendered to a U.S. naval vessel tailing the lifeboat before the dramatic rescue.

Phillips's vessel, the Maersk Alabama, was taken by the pirates five days earlier after he surrendered himself in exchange for the safety of his 19-member crew.

As Phillips's crew celebrated his freedom on Tuesday, the vessel's chief mate urged strong U.S. action against piracy.

"It's time for us to step in and put an end to this crisis," Shane Murphy said. "It's a crisis. Wake up."

The freed captain and crew were due to be reunited with their families and loved ones in the United States on Wednesday, Maersk said.

In a separate rescue last week, French commandos stormed a yacht to free two French couples and a three-year-old child, killing two of their Somalian captors and one of the adult hostages.

With files from the Associated Press