Egypt has begun constructing a huge metal wall along its border with the Gaza Strip as it attempts to cut smuggling tunnels, the BBC has learned.
When it is finished the wall will be 10-11km (6-7 miles) long and will extend 18 metres below the surface.
The Egyptians are being helped by American army engineers, who the BBC understands have designed the wall.
The plan has been shrouded in secrecy, with no comment or confirmation from the Egyptian government.
The wall will take 18 months to complete.
For weeks local farmers have noticed more activity at the border where trees were being cut down, but very few of them were aware that a barrier was being built.
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