KHARTOUM - The head of Sudan's opposition political alliance, freed after two days in detention, said on Sunday that the government fears rising popular discontent in the crisis-hit nation.Farouk Abu Issa, who represents more than 20 opposition parties, told AFP he was released on Saturday by the National Intelligence and Security Service (NISS)."They are scared because the country is in a real crisis," he said."They are scared that I am head of the opposition, and they are scared that the opposition will move" into action.Issa said he was held after giving a "fiery" speech in support of four dead Darfuri students.The deaths, following a crackdown on a tuition protest at Gezira University south of Khartoum, last week sparked the largest outpouring of Arab Spring-style discontent in Sudan since anti-regime protests in June and July.Issa blamed the deaths on Islamic militia."I accused them of killing these boys," he said.But security agents who detained him made only brief reference to his speech, because no charges were ever brought against him or a proper questioning conducted, he said, adding that he was detained and then freed three times between Thursday and Saturday.Each time he was left sitting in a chair for seven to 10 hours "without anyone talking to me or interrogating me," he said."They asked me to come this morning and I refused," he said. "I asked them, if they have a charge, to take me to court."Issa says his alliance, which includes all major parties except the ruling National Congress, favours peaceful change through strikes and demonstrations, yet he admitted such actions have been rare."I think in the coming few weeks you will see more of them," because although people are still afraid of the security forces the worsening economic situation will force them to speak out, he said."All the people of Sudan are against the regime," Issa said. "The regime is isolated, and they are ruling this country through their security forces."In June and July, demonstrations began at the University of Khartoum over high inflation and then spread to involve scattered protests throughout the country, calling for the fall of President Omar al-Bashir's 23-year government.They petered out following a security clampdown.Inflation has risen further to 45 percent in October, but the cash-starved government has rejected workers' demands to raise the minimum wage to 425 pounds a month (around $65).The deaths of the students, originally from the conflict-plagued Darfur region, led to protests last week by hundreds of people who called for "revolution." The Darfur Students Association has said the four went missing - and were later found dead - after taking part in a peaceful sit-in which was disrupted by the pro-government student union.They were protesting for their "right" to free education, the association said.University officials say the four students drowned.