Four Arabs were killed and nine others wounded Saturday in an explosion and the subsequent collapse of two Egypt-Gaza smuggling tunnels, often used by terrorists.

The tunnels were dug under the border. One of them was under the city Rafiah, part of which is located in Hamas-controlled Gaza and part of which is under Egyptian sovereignty.

Two workers were killed and seven were wounded when a gas balloon exploded in the Rafiah tunnel. Another nearby tunnel caved in, killing two workers and injuring two others.

The smuggling business has declined sharply since Israel has removed all limits on the overland transport of goods and material to Gaza except for weapons, explosives and select dual-purpose goods commonly used in weapons manufacture.

The explosion and collapse confirm IDF warnings that Hamas is stockpiling more advanced weapons. Israeli airplanes have been warned not to fly too close to Gaza because of intelligence information that terrorists possess advanced anti-aircraft missiles that can down a commercial airplane.

Egyptian police on Friday discovered three new tunnels at the border and raided them, confiscating merchandise.

Tzipi Livni, when she was Foreign Minister in the Olmert government in early 2009, agreed to end the Operation Cast Lead counterterrorist campaign in return for American guarantees that monitoring devices would be installed to stop smuggling.