"There was foreign support for the attacks that aimed at breaking the will of the people and the army," Sisi was quoted as saying by ahram online news website today.
His remarks came after convening emergency meeting with the Armed Forces Supreme Council here this morning. Following the attack, the country has announced a three-day national mourning period.
"No one can break Egyptians nor the army determination," Sisi said.
"Since before 3 July, 2013 we had a choice - either the people or the army would have to confront terror. We chose that the army carry out the mission," Sisi said.
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"Egypt's sons of the army have sacrificed their lives for the sake of this country to live," Sisi said.
Two separate terrorist attacks close to the Israeli and Gaza Strip borders in the restive North Sinai province yesterday killed at least 31 soldiers and left 26 others injured, prompting the government to declared a three-month state of emergency.