GAZA CITY, Gaza Strip (AP) – An explosion collapsed a tunnel under the Gaza-Egypt border early Friday, trapping five militants inside and killing at least one, Palestinians said.

The Al Aqsa Martyrs’ Brigades, a violent offshoot of the Fatah movement of Palestinian President Mahmoud Abbas, said the five were members. The group refused to say what they were doing.

The militant group said the explosion was not caused by an Israeli airstrike, after first blaming Israel. The Israeli military said it had no forces inside Gaza and denied involvement in the incident.

Israel often attacks tunnels under the border, saying they are used for smuggling weapons and explosives into Gaza.