(Reuters) - Fifty international aid groups and United Nations agencies issued a joint appeal on Thursday calling on Israel to lift its blockade of the Gaza Strip, which is ruled by Hamas Islamists.

"For over five years in Gaza, more than 1.6 million people have been under blockade in violation of international law. More than half of these people are children. We the undersigned say with one voice: ´end the blockade now,´" the petition said.

Amongst the signatories were Amnesty International, Save the Children, the World Health Organization, Oxfam, the Office of the High Commissioner for Human Rights and five other U.N. bodies.

Israel imposed restrictions on trade to Gaza in 2001 following the outbreak of a Palestinian uprising and tightened them further in 2007 after Hamas seized power in the coastal enclave adjacent to Egypt, which also enforces a blockade.

It has relaxed them over the past two years in the face of heavy international pressure, but insists on checking all goods entering the territory to prevent arms, or weapons-making equipment, from reaching Hamas.

"All cargo going into Gaza must be checked because Gaza is controlled by Hamas, an internationally recognized terrorist organization," said Mark Regev, spokesman for Israeli Prime Minister Benjamin Netanyahu.

"Just this morning an Israeli farmer who was ploughing his field was shot at from Gaza. Is it really fair to expect Israel to remove the restriction on military use items while the regime in Gaza is as hostile and aggressive as it is to Israel?"

Hamas´s founding charter calls for the destruction of Israel, but its leadership has raised the possibility of entering into a prolonged truce with Israel after years of bloodshed. (© Thomson Reuters 2012. 06/14/12)