President Abdel-Fattah El-Sisi said that a series of militant attacks that killed at least 30 people in Sinai on Thursday are "the price Egyptians are paying" for ousting the Muslim Brotherhood from power in 2013.

El-Sisi strongly condemned the attacks, saying that Egypt is facing a war against "the strongest secret organisation of the last two centuries", an apparent reference to the Muslim Brotherhood.

In comments reported by state-run news agency MENA, El-Sisi said that had Egyptians not "gone out against" the Muslim Brotherhood during the presidency of Mohamed Morsi, they would be facing "a far greater price."

Morsi was ousted from the presidency in July 2013, after mass protests against his rule.

Officials accuse the Brotherhood of orchestrating and supporting violent militant attacks in Sinai, although the organisation's representatives have denied any links with the violence.

Sinai-based militant group Ansar Beit Al-Maqdis claimed responsibility for Thursday's attacks on an affiliated Twitter account.

An exact death toll has not been released by military officials, but media reports suggest at least 30 died in the attacks, including civilians.

“The blood of 90 million Egyptians is very precious to us, and we will get revenge for all those who died for their country,” said El-Sisi.

El-Sisi was speaking in Addis Ababa, where he was due to attend the African Union summit. He cut his visit short and return to Cairo following Thursday's spate of violent attacks, MENA reported.

The Egyptian president also said that a major investment conference scheduled to take place in Sharm El-Sheikh in March will go ahead as scheduled, despite the violence. The three-day conference aims at reinvigorating foreign investment in an economy that continues to suffer from four years of turmoil.