Israel's offensive against the Iran-backed Hezbollah militia has thrust the UNIFIL force deployed in Lebanon since 1978 into the spotlight.

The force, which involves about 9,500 troops from some 50 nations led by a Spanish general, has in recent days reported multiple Israeli attacks that injured five of its troops and sparked international condemnation.

On Sunday, Israeli Prime Minister Benjamin Netanyahu called on UNIFIL to withdraw for their own safety and said their presence had "the effect of providing Hezbollah terrorists with human shields".

Spain condemns Netanyahu's call for the force to pull back and "there will be no withdrawal of UNIFIL", Sanchez told a forum in Barcelona.

Sanchez affirmed his commitment to a 2006 UN Security Council resolution agreed after the last major Israel-Hezbollah conflict, which stipulated that only the Lebanese army and UN peacekeepers should be deployed in south Lebanon.

That commitment "makes more sense today than ever after seeing what is happening on the ground", Sanchez said.

Israel's committed an "unacceptable" violation of international law and Spain will continue contributing to the force "because we have a firm and clear commitment to peace", Defence Minister Margarita Robles told reporters in Madrid.

Sanchez has become a strident critic of the Netanyahu government's war in Gaza, which was sparked by last year's unprecedented Hamas attack on Israel.

The war has drawn in Iran-backed groups from across the region including Hezbollah, with Israel last month escalating its cross-border fire with the group and launching a ground offensive in southern Lebanon.