Israeli ground forces entered the Gaza Strip on Thursday evening after finding a large tunnel filled with explosives running beneath the border fence with the Hamas-controlled enclave.

Soldiers conducting routine patrols of the border near the town of Nirim found a smuggling tunnel 4 meters deep and almost 5 meters wide burrowed beneath the border, the IDF Spokesperson said.

Nirim was the scene earlier in the day of an incident in which terrorists in the Gaza Strip fired on a work crew and IDF troops returned fire.

The patrol that discovered the tunnel crossed into the Gaza Strip to search for explosives, and, on their return, while repairing the border fence, an “extremely large” amount of explosives detonated on the Gaza side of the border. One soldier was very lightly injured, and an IDF jeep was damaged by the blast that reportedly launched it 20 meters.

“It’s a very large smuggling tunnel, unlike anything we’ve seen recently,” the spokesperson’s office said.

The troops ventured some 200 meters into the Strip, a rare move along the tense border.

Hamas’s military arm claimed responsibility for the explosion on their website, saying the blast was caused by a roadside bomb.

The Izz al-Din al-Qassam Brigades said the blast came in response to the death of an 13-year-old boy earlier in the evening. A health spokesman, Kamal Mousa, said Humeid Abu-Daqa died after a bullet in the same area hit him.

Late Thursday night, Defense Minister Ehud Barak said Israel considers the incident a serious event, holding Hamas responsible and adding that Israel will determine when and how to respond.

The army suspected that the tunnel was part of a “kidnapping attempt” or an attempt to kill IDF soldiers stationed along the border. In the past two weeks there have been three cases of explosives placed on the border injuring Israeli soldiers.

The IDF spokesperson confirmed that the explosion occurred in the vicinity where, earlier in the evening, Palestinian medical sources reported a 13-year-old Palestinian boy was killed by Israeli fire.

The IDF had no information indicating its troops targeted anyone, and reported that there were no suspicious persons in the area when soldiers conducted their mission.

The spokesperson also could not confirm a report in Palestinian Wafa news agency that Israeli tanks and bulldozers entered the Gaza Strip on Thursday when the boy was killed.

GOC Southern Command Maj. Gen. Tal Russo was expected to publish an operational assessment of the incident on Friday.

In June 2006, Palestinian terrorists crossed into Israel from Gaza via an underground tunnel near the Kerem Shalom crossing, attacked an Israeli army position, killed two soldiers and captured a third, Gilad Shalit. Shalit was dragged back into Gaza and held captive by Hamas for more than five years. He was released in a lopsided prisoner exchange in October 2011 under which Israel also freed more than 1,000 Palestinian security prisoners.

Hamas and other Gaza terror groups have repeatedly vowed to kidnap more Israeli soldiers in order to pressure Israel into releasing further security prisoners, including the orchestrators of major suicide attacks in Israel whom Israel balked at releasing in the Shalit exchange.

AP contributed to this report.