CAIRO -- Suspected militants attacked a bus carrying Egyptian soldiers in the northern Sinai peninsula on Sunday, killing four of the conscripts and injuring 13 others, state media reported.

The attack brought the military’s two-day death toll in the restive peninsula to nine. Five Egyptian soldiers were killed in a helicopter crash Saturday; a Sinai-based militant group claimed it had shot down the chopper.

The military did not immediately say why the helicopter crashed. If the claim by the group, Ansar Bayt al-Maqdis, or Partisans of Jerusalem, is true, the downing of the chopper marks a new measure of sophistication on the part of Islamic insurgents battling Egyptian forces in the peninsula.

Until now, there has been no indication that the group possessed or was willing to use surface-to-air missiles, said David Barnett, a research associate at the Foundation for Defense of Democracies who studies militant groups in the Sinai. Such a development would be militarily important because of the significant role of helicopters in Egyptian operations in the northern Sinai, he said.

It could also carry damaging repercussions for the tourist industry in the southern part of the peninsula and on the Red Sea, Barnett said. Egypt’s tourist industry has cratered during the last three years of political upheaval, but these resorts have retained some appeal, in part because they are seen as distant from turmoil in Cairo.

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