UPDATE 8-Somali pirates seize two more ships, others attacked

* Pirates launch night attack on Greek bulk carrier

* Another pirate gang seizes Togo-flagged cargo ship

* Pirates also shoot at U.S.-flagged vessel

* U.S. military reviewing strategy against piracy

(Adds attack on U.S.-flagged ship)

By Alison Bevege

ON BOARD CORTE-REAL, April 14 (Reuters) - Somali pirates hijacked two more cargo vessels and opened fire on two others on Tuesday in attacks that showed a determination to go on striking at shipping on the region's strategic trade routes.

The capture of the Greek-owned MV Irene E.M. and Togo-flagged MV Sea Horse were a clear sign pirate gangs have not been deterred by two raids in recent days in which U.S. and French special forces have killed five pirates.

NATO Lieutenant Commander Alexandre Fernandes said the Portuguese warship Corte-Real had received a pre-dawn distress call from the St. Vincent and the Grenadines-flagged Irene E.M. as it travelled through the Gulf of Aden.