In Algeria, thousands of people demanding democratic reforms defied a government ban on protests and clashed with heavily-armed police in a march in Algiers. Security forces attempted to seal off the city to stop busloads of demonstrators from reaching the capital, yet thousands still managed to flood the city's main squares. A human rights activist said more than 400 people were arrested, including women and foreign journalists. He estimated that up to 28,000 riot police were deployed in the capital, where they charged the crowd to disperse the demonstrators. Organisers said 10,000 people took part in the protest, but officials put the turnout at about 1,500. In Yemen, 2,000 protesters marching for democracy and an end to the leadership of president Ali Abdullah Saleh were attacked by government supporters armed with knives and batons as they chanted "The people want the fall of the government" and "a Yemeni revolution after the Egyptian revolution" in the capital, Sanaa. Saleh, trying to ward off the protests spreading across the Arab world, has promised to step down when his term ends in 2013, but the opposition has yet to respond to his call to join a unity government. Some 300 anti-government student demonstrators assembled at Sanaa University yesterday morning. As numbers swelled into the thousands, they began marching towards the Egyptian embassy, where they were confronted by pro-government supporters, who attacked them. Two people were injured. In Egypt itself, protesters continued to celebrate after Friday's dramatic events, while clearing up Cairo's Tahrir Square, which has been the focus of 18 days of protest. Although Egypt's new rulers, the national army council, pledged to hold elections, some demonstrators vowed to stay until all their demands for constitutional change were met. With one eye on the global picture and relations with Israel in particular, a spokesman for the Armed Forces Supreme Council said its members would continue to honour Egypt's international obligations. On state television, he said the military was "looking forward to a peaceful transition, for a free democratic system, to permit an elected civil authority to be in charge of the country, to build a democratic free nation". In London, thousands of supporters packed into Trafalgar Square to celebrate Mubarak's departure.The rally - one of 46 held yesterday in 16 countries by Amnesty International - was organised before Mubarak resigned and had been planned to increase international pressure for change. Amnesty secretary-general Salil Shetty told the crowd: "We want to send a resounding message from Trafalgar Square to Tahrir Square that we are in solidarity with the people of Egypt." Meanwhile, Foreign Secretary William Hague said the ousting of Mubarak should "jolt" Israelis and Palestinians to get round the negotiating table in a renewed bid to find a Middle East peace settlement. Hague acknowledged that events in Egypt and Tunisia, where president Zine al-Abidine Ben Ali has also been forced out in a popular uprising, could complicate the search for a peace deal. However, Hague warned also that time was running out for an agreement based on a two-state solution as Israeli settlements continue to encroach into occupied Palestinian territories. Israel in particular had seen Mubarak as a stabilising force in the region, acting as the guarantor for the past 30 years of the historic Israeli-Egyptian peace treaty. Hague insisted that Israel should not fear the rise of democracy in the Arab world and he called on Israelis to join the Palestinians in a return to the direct talks, which broke off last September. "What we should be afraid of here is not democracy but uncertainty and instability that can make national leaders more cautious and say that we are only going to deal with one thing at a time," he said. "Perhaps one of the good things that might come from events in Egypt and Tunisia is that policymakers in Israel and among Palestinians will be jolted to see that it is vital now to take this forward because in a few years' time a two-state solution will be much, much more difficult to achieve."