Egyptian security forces have uncovered a tunnel stretching under the Gaza-Sinai border lined with iron.

The finding may mark the most advanced tunnel yet located by Egyptian forces in a two-year campaign to seal the border between Egypt and the Palestinian territory. Thousands of tunnels have been demolished in the campaign, while homes above ground were removed to create a “buffer” zone inside the city of Rafah, which straddles the border.

The tunnel was over 200 meters (650 feet) long, the Palestinian news agency Maan reported. Its walls were 40 centimeters (16 inches) thick.

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Destroying it required an unusually large quantity of explosives, according to a report in the Ynet news site.

The tunnels once constituted Gaza’s economic lifeline to the world. Their destruction has worsened conditions in the Hamas-ruled strip, which is also under an Israeli blockade after multiple rounds of war in recent years with the Jewish state.

Hamas has been at odds with Egypt’s new government, led by Abdel-Fattah El-Sissi, after siding with the Muslim Brotherhood after the 2011 ouster of Egyptian strongman Hosni Mubarak.