US Ambassador to Israel Dan Shapiro visited the Hamas attack tunnel leading from the southern Gaza Strip into Israel on Thursday.
The IDF uncovered the 1.7-km long tunnel on Sunday.
The tunnel might have been intended for attacking or kidnapping soldiers, or for moving terrorists from Gaza into Israel to commit an atrocity against civilians in border towns and villages, army sources said after the discovery.
A statement from the US embassy in Tel Aviv stated that the ambassador's visit demonstrated "US support for Israel's security and its right to defend itself."
"I was shocked from what I saw in the tunnel. It is clear that this tunnel has only one purpose: to carry out terrorist attacks against Israeli civilians and IDF soldiers," Shapiro said in the statement.