US Secretary of State Hillary Clinton meets Egypt's Muslim Brotherhood president Mohammed Morsi in historic first Her two-day visit - during which she will also meet Field Marshal Hussein Tantawi, the country's interim military ruler after the Mubarak regime was ousted in last year's revolution - comes at a crucial moment for Egypt's new Islamist president. Pressure is growing on him to begin rooting out powerful old regime figures, after the first act in a confrontation with the army in Cairo last week. Both the secular revolutionaries who crowded into Tahrir Square last year and younger members of the Muslim Brotherhood want him to embark quickly on ousting the so-called "feloul," the civilian and military officials "left over" from three decades of Mubarak's rule. Their demands threaten a new round of turmoil, 18 months after the uprising that drove the disgraced former president from power. "President Morsi has been elected and now he is on his way to take power from the military, and we are behind him," said Assem Farag, 32, a driver, at a Muslim Brotherhood-organised rally in Tahrir Square on Friday night. All the obstacles in Morsi's way are figures from the old regime trying to stop him. We will gradually push them out. The generals of the Supreme Council of the Armed Forces (SCAF) who have run Egypt since Mubarak's downfall in February 2011 are now in an uneasy power-sharing arrangement with the newly elected president. The relationship has rapidly changed since he accepted office. Only two weeks ago Muslim Brotherhood stewards stopped their brethren from chanting slogans against the army at demonstrations. But on Friday speakers openly condemned Field Marshal Tantawi, the powerful head of the armed forces, as thousands crowded into Tahrir Square. The atmosphere in the square has changed markedly from the days after the revolution. Now, men with beards predominate; the few women present are all in headscarves; and stalls sell pictures of the new Muslim Brotherhood president alongside nooses for hanging manikins of Mubarak. The angrier new mood follows the first act in what looks like a battle for Egypt's soul, a long-expected confrontation between the army and Muslim Brotherhood - the two most powerful forces in post-revolution Egypt. Just a week after his inauguration Mr Morsi threw down a gauntlet to the army and recalled parliament - against the wishes of SCAF. But after he was overruled by judges of the Supreme Constitutional Court - mostly leftovers from Mubarak days - he appeared to blink first and backed down, postponing the power struggle for now at least. But it was significant that the first act of the new president had been to express his defiance of the army, signalling what his supporters hope will be a campaign of attrition against the informal networks of old regime appointees. Generals, judges, top civil servants and businessmen appointed or made rich by Mubarak still control real power. Many are wealthy, and nearly all are deeply opposed to changing the corrupt system which has suited them well. Through SCAF, the army is by far the strongest element of the old regime still in power: it controls the budget and has the power to declare war and set foreign policy. It will continue to do so at least until new parliamentary elections are held, expected in about six months, and a new constitution is drawn up. Drafting that, and setting limits on the power of the army, is likely to prove the major battlefield for the two. Radical young Muslim Brotherhood members who took part in last year's revolution have shown a surprising willingness to force the pace of change. Thousands of people were in the street supporting Dr Morsi last week when he challenged the army. He is a true revolutionary," said Dr Ahmed Akeel, 34, a prominent member of the Brotherhood. He will finish the goals of the revolution and help us achieve a full democracy. I believe Mohammed Morsi is determined, and has the support of the people that he needs, to get this job done. Dr Akeel said an estimated 1,500 powerful figures from the former regime remain in place, including soldiers, ex-members of Mubarak's National Democratic Party, and businessmen, still supported by thousands more policemen and thugs. "There were institutions which were corrupt under the former regime and there is now a demand from the people to purify them," he said. Now some Egyptians fear elements who fear an Islamic takeover may rally to the side of the army, with the potential for new clashes. Across Cairo from Tahrir Square, by the memorial to the former President Anwar Sadat who was assassinated by Islamic terrorists in 1981, daily rallies are now held in support of SCAF. Waving national flags, and with martial music blaring out, demonstrators castigate the Brotherhood and praise the army, which for all its wealth and privilege still enjoys wide support among Egyptians. Thousands of demonstrators attend nightly, including well-dressed families and many who thronged Tahrir Square last year during the revolution. "We hate the Muslim Brotherhood, they are liars and hypocrites, and they don't know anything about democracy," said Abdul Salem, 50, a lawyer, on Friday evening. Another demonstrator, Noura Mohammed, wearing a traditional black head-dress, said: "Morsi is too extremist for Egyptians. We support the army - they are faithful to the people. We are behind our army. Opponents of the Brotherhood fear that it will use its networks of grassroots supporters to try to change Egyptian culture, slowly reshaping society in its own image. Already gangs of devout young men in villages and slums have taken on a more active self-appointed role in policing their communities. Customers at shops selling alcohol are being abused, and in one horrifying case last week a man bled to death after he was stabbed in the groin as he promenaded with his fiancée. His attackers, self-appointed religious police, were arrested; they were not Muslim Brothers, but extremists who seem to have taken heart from Morsi's success in the polls. "Before Morsi was elected we were used to sexual harassment, but now we get a lot of verbal harassment if we go outside without a headscarf," said Theresa Samir, 24. There is real fear among some unveiled women, I even know a few who hardly leave their homes.