The IDF struck a smuggling tunnel, killing two Hamas members and reportedly injuring 21 others.
Which means that it was a tunnel for smuggling weapons.
Of course, being the liars they are, the Gazans are accusing Israel of somehow injecting poison gas in the tunnels as they were bombing them.
UPDATE: Ma'an reports that Hamas is claiming not that Israel bombed the tunnel today, but that Hamas members went to inspect a damaged tunnel and died from inhaling poisonous gas. (h/ t Tam)