Four soldiers were killed and 12 others wounded in separate attacks by the Yemeni southern separatists, the Defense Ministry and local media said on Tuesday. In an ambush in the southern province of Lahj late on Monday, gunmen killed four security soldiers and wounded nine others, said the Defense Ministry. 'Four security soldiers were killed and nine others wounded late on Monday when gunmen of the southern separatist group ambushed their patrol car and opened fire at them,' said the ministry, citing Colonel Ali Muthanna, the security director of Halimain district in Lahj. 'We dispatched the patrol car to inspect the cutoff in a telecommunication cable in Helya area after we were informed that a group of separatists were behind the act,' said Muthanna. 'The separatists ambushed the patrol car before the car deflected off its way and collided with a lorry,' he added. The Defense Ministry said the attack took place a day after the Yemeni President Ali Abdullah Saleh ordered the release of 52 southern outlaws who were arrested on charges of involving in blocking roads and stirring up riots. In a separate incident in the southern troubled province of al- Dhalee, three policemen were injured late on Monday when separatists hurled grenades and mortar shells on the police and security facilities in the capital city of al- Dhalee, official Saba news agency said on Tuesday, citing Ali Saleh al-Azraqi, the police director there. Voices to secede the southern part of the country from the north increased recently along with separatist ambushes and clashes against government troops which lead to many fatalities on both sides. Northern and southern parts of Yemen were unified in 1990 according to a deal between the People's General Congress and the Yemeni Socialist Party. However, the deal fell apart, leading to a crisis between the two allies, which developed into a civil war in 1994. 