A Pakistani soldier displays hand grenades recovered during an operation against terrorists in northwestern Pakistan's Khyber Agency, Oct. 8, 2015. (Xinhua/Umar Qayyum)

LISBON, July 4 (Xinhua) -- Portuguese President Marcelo Rebelo de Sousa has called for an immediate investigation into the recent theft of a large quantity of hand grenades and other military equipment from an arms depot in the center of Portugal.

The haul was found to be missing on Wednesday from a weapons storage unit in Tancos, some 130 km northeast of Lisbon after military personnel conducting a routine patrol of the premises discovered evidence of a break-in.

Rebelo de Sousa is demanding a full investigation into the arms theft, which is reported to have comprised 57 kg of plastic explosives, a quantity of tear gas, 44 rocket launchers and over 130 hand grenades.

Commenting on the theft, the Portuguese president said: "Undoubtedly, we must thoroughly investigate all the facts and responsibilities concerning this case," adding that "similar incidents have been reported in other NATO countries over the past two years, one of which happened only a few months ago," without specifying the countries in which these incidents took place.

Following a meeting with United Nations Secretary-General Antonio Guterres on Monday, Portuguese Foreign Minister Augusto Santos Silva said the incident was "very serious" and that "every possible effort is being made to recover the stolen equipment."

Five Portuguese generals based at Tancos depot have been temporarily relieved of their duties pending an investigation, while border patrols and other security forces around the country have been put on maximum alert.