Somali pirates are extending their activities further out from the Somali coast, beyond the Seychelles in the east and to the Red Sea in the north, warns an international naval task force.

The force has urged mariners to take advantage of the monsoon season about to  begin, which will hinder pirates' activities until September.

In a special advisory issued to shipping Wednesday, the Combined Maritime Forces (CMF) of a number of Western powers noted that most attacks on ships in the past two years have taken place during daylight hours in the Gulf of Aden.

"However, recently pirates have attacked vessels at night and have conducted attacks far off the eastern coast of Somalia," the CMF said. Using "mother ships" as staging platforms, they are able to operate much further from the Somali coast than before.

The force also said a confirmed pirate attack in the southern Red Sea created "a new area of potential risk."

"Merchants [ships] are urged to use the weather to their advantage, planning new routing off the east coast of Somalia due to the start of the southwest monsoon season...

"Pirates have also recently increased their number of attacks during the hours of darkness, highlighting the need for heightened vigilance of merchant mariners during both day and night time transits through the high risk areas."