Egypt's President Abdel Fattah el Sisi has defended his recent decisions to partially scrap subsidies on fuel, calling them a necessary "bitter pill".
In a nationally televised speech on Monday, Sisi said he could not delay such decisions even if it cost him support because "the dangers are great" for Egypt's economy.
He approved this weekend fuel-price increases as high as 80 percent. The decision shocked many in the country where nearly 50 percent live in poverty.
Comparing the current conditions to times of wars with Israel, Sisi said Egypt is at war to rebuild following turmoil.
He urged Egyptians to bear the austerity measures and appealed to the rich to donate to Egypt's development.
His speech came just hours after a spokesperson for the opposition 6 April Movement said that police had arrested Mohamed Nassar, a political activist, for holding a banner in Cairo that read "You [president] promised not to remove the subsidy, but you turned out to be a liar".
"Mohamed Nassar has been arrested and he is now in Qasr al-Nil police station," Mohamed Fouad, the spokesperson, said on Monday on his Facebook page, as reported by Al-Masry Al-Youm paper.
"Mohamed held the banner and stood alone in Tahrir Square."
According to Fouad, a police report was filed accusing Nassar of spreading rumours and harming public peace. He was referred to prosecution on Monday.
The 6 April Movement played a key role in mobilising support for the 2011 revolution against President Hosni Mubarak's rule.
It later joined calls for the unseating of the elected Islamist President Mohamed Morsi last year and supported the his army-led overthrow.
However, the 6 April Movement quickly turned against the military-installed regime amid an intensified crackdown against dissent.
Addressing world powers during Monday's speech, Sisi said that self-declared jihadist fighters were ravaging the Middle East and posed a threat to everyone's security.
"Be alert to what is happening in the region ... . This region is being destroyed right now and we should not let this happen," he said.
Naming the US, Russia, China and Europe, Sisi said: "This matter concerns not just the Arab world. It concerns the entire world."
Fighters have long challenged pro-Western Arab countries, and Egypt itself faces an insurgency based in the Sinai Peninsula.
But a rapid advance by the Islamic State through major oil producer Iraq has rung alarm bells from Cairo to Washington.
The al-Qaeda offshoot declared itself a "caliphate" last month, weeks after overrunning the northern city of Mosul and seizing an expanse of land north and west of Baghdad.
Sisi did not name the Islamic State group in his speech, but the mention of "countries that are being destroyed and divided in the name of religion" was a clear reference to their actions in Iraq and neighbouring Syria.