The Islamic militant group Hamas says a group of militants have gone missing inside a tunnel built to attack Israel that collapsed due to heavy rainfall.

Hamas confirmed the incident in a statement Wednesday, a day after Palestinian social media activists publicized the matter.

Hamas, which controls the Gaza Strip, has built a sophisticated network of tunnels that it has used to hide weapons, fire rockets into Israel and penetrate Israel to carry out attacks. Israel destroyed dozens of tunnels in its 2014 war with Hamas in Gaza.

Palestinian activists say the tunnel was in northern Gaza and that at least seven militants were inside when it collapsed Tuesday. Hamas says it is searching for the missing.

Three Hamas militants were killed in other tunnel collapses in Gaza this month.