Egyptian President Hosni Mubarak has said he will not stand for re-election in September, as protests against his rule grow. Speaking on state TV, Mr Mubarak promised constitutional reform, but said he wanted to stay until the end of his current presidential term. The announcement came as hundreds of thousands rallied in central Cairo urging him to step down immediately. Later violent clashes erupted in the second city Alexandria. Shots were fired, as al-Jazeera TV showed apparent street battles between Mubarak supporters and anti-government protesters, as a tank advanced towards them and then withdrew. The Cairo and Alexandria demonstrations were the biggest since protests began last week. The BBC's Yolande Knell in Cairo's Tahrir Square says it remains to be seen whether Mr Mubarak's statement is enough for protesters, and adds that it could divide Egyptians. She says there are some determined to carry on, while others think these are major concessions and that the protests have gone far enough. 'I will die here' In his address, Mr Mubarak said he would devote his remaining time in power to ensuring a peaceful transition of power to his successor. "My first priority is to restore peace and stability in our country, to ensure the peaceful transition of leadership, and to ensure that the responsibility goes to whomever the people of Egypt choose in the next election. I do not intend to stand for election again," he said. But he criticised the protests, saying what began as a civilised phenomenon turned into a violent event controlled by cowards. "The events of the past few days require us all - people and leaders - to make the choice between chaos and stability, and dictate new conditions and a new Egyptian reality," he said. He said he had offered to meet all parties but some had refused dialogue. Mr Mubarak ended his speech by saying that he would not leave Egypt. "This is my country. This is where I lived, I fought and defended its land, sovereignty and interests, and I will die on its soil," he said. Opposition politician George Ishak expressed dismay at the speech. "We are very disappointed and we are very angry. We have very clear demands and he denied everything that we demanded. He has to go now. I am afraid now of what will happen in the future," he told the BBC. Leaders of the protests had called on Mr Mubarak to step down by Friday, when demonstrators were planning to march on the presidential palace. Army vow Mr Mubarak's speech came after a meeting with US special envoy Frank Wisner, who was said to have urged the president to announce his departure. But the BBC's Kim Ghattas in Washington says that while this address would have been acceptable a week ago, US officials believe that it is now too little too late and Mr Mubarak should leave now. US President Barack Obama is expected to make a statement about the developing situation shortly. Meanwhile the UK foreign office said it was studying Mr Mubarak's proposals, but that the real test was whether Egyptian people's aspirations were met. Journalists in the square estimated hundreds of thousands of people had joined the protest by its peak mid-afternoon. Correspondents say that hours after dusk and despite a theoretical 1500 (1300 GMT) curfew and bitter cold there were still large crowds, though many people had drifted home. Many carried placards and banners daubed with anti-Mubarak slogans. Egypt's powerful army has vowed it will not use force against the protesters, despite maintaining a strong presence in central Cairo. Further protests were reported in Suez, Mansoura, Luxor and Assiut. Mr Mubarak reshuffled his cabinet on Monday to try to head off the protests, replacing the widely despised Interior Minister Habib al-Adly. Source: BBC