ADEN, 23 May -- Security authorities in the southern port city of Aden Saturday arrested 428 people on charges of taking part in an illegal demonstration organized by the southern political movement to protest state policies, the official website of Yemen’s Socialist Party said. The demonstration was held as the country was celebrating its 20th anniversary of national unity and of the 428, 265 were imprisoned in al-Mansoura central prison, 42 in Sheik Othman police prison, 36 were taken into custody at Tareq military compound, 10 in the prison of Kreter and the remaining 75 were scattered among different prisons across the city. President Ali Abdullah Saleh granted on Saturday amnesty to all prisoners from the southern movement. Meanwhile, the ministry of interior Sunday said in a statement posted on its media center website that security services in the southern region of Abyan arrested a man suspected of making explosive bombs,” adding “his arrest came after investigations confirmed his involvement in bomb making.” A security source told Agence France Presse the man is a member of the southern political movement, adding “he confessed that his mission was confined to making explosives and delivering them to persons who carry out acts of sabotage in some southern cities in the provinces of Lahj, Abyan and al-Dhala.” Meanwhile, Oil Minister, Ameer Salam al-Aidrous Sunday said “Yemen was going through a critical stage that threatened its unity, but I think it passed it,” adding “Yemen is way stronger than depicted in foreign reports.” Al-Aidrous who was talking in an interview with the Saudi-owned London-based al-Sharaq al-Awsat newspaper said “there are more than 22 international companies operating in the oil sector in Yemen and these companies never stopped working and producing oil for a single day and that testifies to the fact that despite the circumstances, the state managed to provide a good atmosphere for investment.” He said oil exists in the provinces of Abyan, Aden and Lahj and “one of Italy’s major international companies is exploring for oil in al-Jawf, Marib, and Shabwa while Hodeida and offshore oil exploration will be added later.” On challenges facing the country, he said “the challenge is the economy and development. There are 22 million people in Yemen and this fast population growth should be met with strong economic growth rates. The southern political movement and others are not new,” adding “we accept peaceful exchange of power through ballot boxes but not through chaos and militancy and as a citizen I reject conflict over power.” He lashed out at Yemen’s Socialist Party (YSP) saying “though it is in the opposition, it is proposing a very dangerous and blunt issue which is the separation.” In other news, Assistant Secretary General of Yemen’s Socialist Party (YSP) Yahia Mansour Abo-Asba rejected on Sunday President Saleh’s offer to form a national unity government, News Yemen website reported. He said his party is “committed to the Joint Meeting Parties (JMP),” but other conflicting reports said YSP leaders are still studying the President’s offer. Meanwhile, the spokesman of the opposition alliance, the JMP, Muhammad al-Naimi said “the opposition higher council will hold a meeting today to discuss the President’s initiative.” Muhammad Mansour, member of the JMP’s council said the opposition is working on a positive response to Saleh’s offer. Meanwhile, Assistant Secretary General of the ruling party, Ahmad Obid bin Dhager said in a statement to the Kuwaiti al-Siyassia newspaper that he hoped the JMP would accept the President’s offer for a national unity government, adding the war with the Shiite rebels in north Yemen is over and the last round was “the last.”