The Israeli military said Sunday it has uncovered a concrete-lined tunnel dug under the border from Gaza into Israel that it alleges could be used to attack or kidnap civilians.
In response ot the discovery, Israel's army has cut off the transfer of all construction materials to the Palestinian territory.
The tunnel runs nearly a mile from a house in Hamas-controlled Gaza to a site close to a kibbutz, Ein Hashlosha, reports the BBC.
According to the Israeli military, it appears to have been recently dug and in use until its discovery last week.
"The tunnel is extremely advanced and well prepared," Brig. Gen. Mickey Edelstein, commander of Gaza Strip division, told reporters.
"Massive amount of concrete and cement have been used to build this tunnel."
An AFP correspondent said the tunnel's walls were reinforced with cement and a man could stand upright in it.
The Israeli military invited reporters into the tunnel and showed them food wrappers, work gloves and a digging tool it said had been found inside, reports the Associated Press. A cookie wrapper the military claims was found in the tunnel is dated June 2013, indicating there were people inside in recent months.
This is not the first tunnel to be found dug under the border between Israel and Gaza.
In a statement, the military made mention of Israeli soldier Gilad Shalit, who was abducted by Palestinian militants and transferred to Gaza via a tunnel in 2006 and held for five years.
Gaza's Hamas rulers accused Israel of "exaggerating things" and "trying to justify the blockade and the continuous aggression on the Gaza Strip," spokesman Sami Abu Zuhri said.
The military wing of Hamas, al-Qassam Brigades, posted a photo of the alleged tunnel on Twitter, which it called a 'resistance tunnel'.
A spokesman for the group, who goes by the name Abu Obaida, said on Twitter that "the minds which manage to dig the tunnel can dig dozens more".
Agence France-Presse contributed to this report.