Hamas leader Khaled Mashaal called on Egypt on Friday to stop building an underground wall along its border with Gaza.
Egypt is constructing an underground barrier to stem Palestinian arms smuggling into Gaza and has played down the scope of the dig on the 14-km (8-mile)-long frontier.
Hamas calls the project a "wall of death" that could seal an Israeli-led blockade by smothering smuggler tunnels from the Egyptian Sinai peninsula.
"We call on the Egyptian leadership to stop building the steel wall along its border with the Gaza Strip," Mashaal said at a conference in Beirut.
"A wall (is erected) between enemies and not between brothers," he said.
Israel has long lobbied Egypt to tackle cross-border smuggling, which supplies Palestinians with both munitions and basic commercial goods lacking in Gaza. Egyptian officials have said steel tubes were being placed at several points along the frontier to form a barrier, but have not elaborated on their purpose.
The anti-smuggling wall sparked violence earlier this month when an Egyptian soldier was killed and four Palestinians were wounded in a gun battle during a protest against the wall.