Hamas on Thursday accused Egypt of further besieging the Gaza Strip by flooding the border area to the south of the Palestinian enclave, which is already under an Israeli blockade.
Egypt has been carrying out digging work in the area for several weeks that Palestinians believe is intended to flood the last remaining tunnels between Gaza and the Sinai, where jihadist fighters have been battling Egyptian forces.
Palestinians fear such moves will further isolate Gaza, where more than 100,000 were left homeless in last summer's war with Israel and which is blockaded by the Jewish state.
Egyptian officials have declined to comment on the work criticised by Hamas, the Palestinian Islamist movement that runs the Gaza Strip, where residents have reported water seeping over the border.
"Why are they digging those trenches and those water pipes around Rafah?" Hamas's chief in Gaza, Ismail Haniyeh, said during a speech to commemorate the Muslim Eid al-Adha holiday.
"And why discard neighbourly relations and the history of Gaza, which has always defended the regional security of Egypt and Arab countries? We are telling our Egyptian brothers: Stop this project. We will do our duty against those who besiege Gaza and plot against it."
Egypt has already established a buffer zone 10 kilometres (6.2 miles) long and half a kilometre wide along its border with Gaza.
Since the ouster of its Islamist president Mohamed Morsi in 2013, Egypt says it has destroyed hundreds of tunnels used to transport militants, merchandise and arms between the Gaza Strip and the Sinai Peninsula.
Hamas lost a major ally in Morsi and has had strained relations with President Abdel Fattah al-Sisi, who overthrew him while army chief.
Tunnels have long been used to transport people and goods in and out of Gaza. Egypt controls the only crossing into Gaza not overseen by Israel.