The Palm Sunday bombings killed 45 people and were claimed by the Islamic State group.
Egypt's Cabinet says the state of emergency will go into effect at 1:00 p.m. Monday afternoon.
The second struck outside Saint Mark's church in Alexandria, killing 17 people after a suicide bomber was prevented from entering the building.
Emergency services had scrambled to the scene when another blast rocked St Mark's church in Alexandria where Coptic Pope Tawadros II had been leading a Palm Sunday service.
In their statement, the terrorist group mentions that crusaders and their apostate allies would have to pay a big debt and that it would be paid with the blood of their children.
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Sunday's attack have left some members of the community wondering whether Egypt's President Abdel Fattah al-Sisi has done enough to protect them. President Mohamed Morsi imposed it in January, and following his ouster, his successor Adly Mansour imposed it in August.
Deflecting Western criticism that he has suppressed political opposition and human rights activists since he was elected in 2014, Sisi has sought to present himself as an indispensable bulwark against terrorism in the Middle East.
Referring to the need for increased security for the 550 churches in Assiut, he said: "Thank God, nothing has happened here so far but we are too little prepared for such events".More news: Indian politicians to face trial over mosque demolition
During their first meeting last week, el-Sissi praised President Trump at the White House.
The attacks challenge Egypt on multiple fronts.
Hundreds gathered outside the Tanta church shortly after the blast, some weeping and wearing black while inside, blown apart pews sat atop tiles soaked with blood.
Graphic images of the attacks quickly spread on social media, depicting blood-splattered stone pillars and scattered bodies.
"There was a huge explosion in the hall".
The attacks on Christians, who make up about 10% of Egypt's population, raised security fears ahead of a visit to Cairo by Pope Francis, the head of the Roman Catholic Church, scheduled for 28 and 29 April.
According to the statement the militants were reportedly planning to attack churches and private property of Christians as well as vital security and economic facilities.
The interior ministry said Abdullah had links with the Islamist militant cell behind the December suicide bombing on Cairo's main Coptic cathedral, an attack also claimed by Islamic State. We also pray for our Coptic Orthodox sisters and brothers who continue to be resilient in the face of ongoing and escalating attacks, and who resist the urge to react vengefully or reciprocally.
The group continues to target security in the Sinai Peninsula nearly daily while carrying out sporadic operations in mainland Egypt.