(Updates with fresh Sharif quotes paras 3-4) By Kamran Haider ISLAMABAD, Sept 9 (Reuters) - Pakistani authorities tightened security at Islamabad's airport and have detained more than 2,000 supporters of exiled former prime minister Nawaz Sharif, his party said on Sunday, the eve of his planned return. Sharif, ousted by army chief General Pervez Musharraf in 1999, says he is determined to fly home from London on Monday to try to end President Musharraf's rule despite an appeal from a Saudi official for him to stay away for the sake of stability. Sharif's return is a serious challenge for Musharraf, who has lost much support since trying to dismiss the country's top judge in March. It comes as Musharraf is preparing to try to secure another term in a presidential election by the national and provincial assemblies some time between Sept. 15 and Oct. 15. A general election is due around the end of the year. Sharif's spokesman, Ahsan Iqbal, said authorities had detained more than 2,000 activists from Sharif's party in Punjab province, Sharif's political power base. "The way the government has acted has proven our point that there is no democracy under Musharraf, there is dictatorship in the country," Iqbal said. "Politically, they are very scared of a big show of popularity upon his arrival". A provincial police official said 250 "trouble makers" had been picked up. Sharif is expected to arrive in Islamabad at around noon (0700 GMT). A security high alert has been declared at the airport which will be largely sealed off. "Security is at high alert and tomorrow visitors won't be allowed in, only people with confirmed tickets," a security official said. Before his departure for home, Sharif told Reuters Television in London, "My security is in the hands of God and of course the people of Pakistan." Asked about the detention of his supporters, Sharif said: "Thousands of people have been arrested but by the grace of God our supporters are in the millions. That is not going to deter us." "TENSION" Musharraf sent Sharif to Saudi Arabia in 2000 as part of what the government says was an agreement that Sharif would stay in exile for 10 years. In return, he avoided a life sentence on hijacking and corruption charges. Pakistan says the Saudi royal family and assassinated Lebanese leader Rafik al-Hariri guaranteed the deal. Sharif said on Saturday he understood the agreement was for five years exile. The Supreme Court last month said Sharif had the right to return and the government should not try to stop him. Saudi intelligence chief Muqrin bin Abdul Aziz and al-Hariri's son, Saad, met Musharraf in Islamabad on Saturday. "We are hoping, we are really hoping, sincerely hoping, His Excellency Nawaz Sharif honours this agreement," Muqrin told reporters. He cited concern about Pakistani stability. The government has not said what it will do when Sharif and his politician brother, Shahbaz, land. "We hope that nothing happens because we're just planning a very peaceful homecoming for him. But if they try to obstruct people going to the airport there may be tension," Iqbal said. The brothers could be arrested -- both face various charges -- or they could be put on an aircraft back out of the country, as Shahbaz was when he tried to come home in 2004. Sharif plans to lead a procession from Islamabad 300 km (200 miles) to the city of Lahore, the capital of Punjab province, his hometown and the country's political nerve centre. Musharraf's ruling party, cobbled together from the remnants of Sharif's party, said on Saturday the brothers should be allowed to return freely and compete in elections. (Additional reporting by Robert Birsel and in London by Siddhartha Dubey)
