Egypt increased pressure on the Muslim Brotherhood on Thursday, detaining at least 38 of its supporters on suspicion of belonging to a terrorist organization the day after it was declared one by the government, security officials said.

Gen. Abdel Fatah al-Sissi, the army chief who led the overthrow of President Mohamed Morsi, an Islamist, said the country would be “steadfast” in the face of terrorism, after a small bomb went off in Cairo, wounding five people.

The government on Wednesday declared the Muslim Brotherhood a terrorist group in response to a suicide attack a day earlier that killed 16 people in a Nile Delta city, accusing the group of carrying out the bombing. The Brotherhood, which claims up to 1 million members, condemned the attack.

The move gives Egyptian authorities wider scope to crack down on the Brotherhood, which propelled Morsi to the presidency 18 months ago but has been driven underground since he was toppled in July.

In Washington, Secretary of State John F. Kerry called Egyptian Foreign Minister Nabil Fahmy and “expressed concern” about the Brotherhood being designated a terrorist organization, as well as recent detentions and arrests in Egypt, State Department spokeswoman Jen Psaki said.

Kerry condemned the bomb attacks but “underscored the need for an inclusive political process across the political spectrum that respects the fundamental human rights of all Egyptians in order to achieve political stability and democratic change,” Psaki said.

Sixteen of the arrests Thursday were in the Nile Delta province of Sharkiya. The state news agency said those held were accused of “promoting the ideology of the Muslim Brotherhood group, distributing its leaflets, and inciting violence against the army and police.”

From now on, anyone taking part in Brotherhood protests will be jailed for five years, Interior Ministry spokesman Hany Abdel Latif said on state television. Prison terms for those accused under the terrorism law could stretch to life behind bars. “The sentence could be death for those who lead this organization,” he said.

Terrorism charges will also apply to anyone who finances or promotes the group “verbally and in writing.” Publication of the Brotherhood’s newspaper, Freedom and Justice, was halted in response to the decision.

The state has accused the Brotherhood of turning to violence since the army toppled Morsi after mass protests against his rule.

The small bomb that went off in Cairo smashed the windows of a bus. Abdel Latif said a similar homemade device was found nearby and dismantled.