It was an unusual and terse announcement: "In accordance with current assessments," the Israel army said on Saturday, the Kerem Shalom Crossing would be closed the next day. There was no further explanation.
Kerem Shalom is one of the Gaza Strip's few lifelines to the outer world and the principal entry point for humanitarian aid.
The mystery was resolved at 7 a.m. Sunday, when Israel announced that its air force had destroyed a tunnel running from the Gaza Strip south into Egypt and north into Israel under the delicate triple-border area of Rafah.
Israeli authorities said the tunnel extended almost 600 feet into Israeli territory and was built solely with the aim of executing terror attacks against Israelis. It was dug below the border crossing, beneath pipes used to transport natural gas and fuel.
Israeli Defense Minister Avigdor Lieberman said the tunnel represented a "blatant violation of Israeli sovereignty. The destruction of the network of attack tunnels is an essential part of our policy of systematically harming Hamas' strategic capabilities."
Hamas is the Islamist militia that rules the Gaza Strip, a tiny Palestinian territory wedged among Israel, Egypt and the Mediterranean Sea.
Countering Israel's accusation that the wide, reinforced shaft was built to smuggle weapons and terrorists into Israel, Hamas claimed the tunnel was intended for smuggling goods.
"We have not encountered a tunnel like this before," said Brig. Gen. Ronen Manelis, a spokesman for the Israel Defense Forces.
The existence of tunnels used to smuggle terrorists into Israel was revealed in the initial days of the 2014 war between Hamas and Israel. During the night of July 21, 2014, two Hamas cells attempted to penetrate Israel. In one of the attacks, 10 Palestinians exited a tunnel wearing full Israeli army uniforms. Seven Israeli soldiers and at least 10 guerrilla fighters were killed during the nighttime combat, which took place in residential neighborhoods of Israeli border towns.
The tunnel bombed on Saturday night is the fourth tunnel Israel has destroyed in recent months.
After several setbacks in detecting tunnels, the Israeli army insisted Sunday that Israel possesses "the most advanced capability in the world to locate underground tunnels" and announced its intention to demolish all of the tunnels extending from the Gaza Strip into Israel by the end of the year.
Less than a week before the arrival of Vice President Mike Pence, the region is once again on the verge of turmoil.
Pence's first stop, Egypt, brokered a faltering reunification agreement signed in October in Cairo between Hamas and Fatah, the internationally recognized Palestinian movement that rules the West Bank. Egypt has been fighting a war of attrition against Islamic State-affiliated militias in its vast Sinai desert, which borders Gaza.
"The Egyptians who negotiated a reconciliation with the Palestinian organization likely never imagined that it would dare cooperate with ISIS and dig a tunnel reaching all the way to Sinai," Ron Ben-Yishai, a military analyst for the Israeli daily Yediot Aharonot, wrote on Sunday, adding that the demolition "is likely to have strategic consequences."
He cautioned that "the tunnel underneath the Kerem Shalom border crossing was an operation of deception not only against the Egyptians, but against Israel too. Hamas likely believed the Israeli army would never imagine it was digging a tunnel under the strip's only lifeline, endangering the population's welfare."
Since President Trump's Dec. 6 announcement recognizing Jerusalem as Israel's capital, there has been an uptick in border violence, with more than 40 rockets and mortars fired at Israel from Gaza. Israel attributes most of the rocket fire to extreme Islamist groups in Gaza that are vying for power with Hamas.