Israel's statement makes it clear that the IDF troops were there to dismantle terrorist infrastructure - by which I think they mean the tunnels. This was allowed under the term of the peace plan.
Earlier today, terrorists fired an anti-tank missile and gunfire toward IDF troops operating to dismantle terrorist infrastructure in the Rafah area, in southern Gaza, in accordance with the ceasefire agreement.
In response, the IDF has begun striking in the area to eliminate the threat and dismantle tunnel shafts and military structures used for terrorist activity.
These terrorist actions constitute a blatant violation of the ceasefire agreement, and the IDF will respond firmly.