At least two soldiers were killed Tuesday when masked gunmen riding on motorbikes attacked a military checkpoint in Yemen\'s southern province of al-Dhalea, a government official told Xinhua. A group of masked gunmen suspected of belonging to an armed faction of the pro-secession Southern Movement attacked a military checkpoint in al-Dhalea province, leaving at least two soldiers killed, the local government official said on condition of anonymity. \"Two soldiers were shot on their chests and died on the spot,\" the government source said, adding that two others were seriously injured in the armed attack. The attack targeted a key checkpoint near an army base in central al-Dhalea province, according to the official. North and South Yemen were unified peacefully in 1990, but their relationship deteriorated in 1994. Calls for separation in the country\'s southern regions were renewed in 2007, as southerners have complained of being marginalized. Pro-secession protests have multiplied in the south amid a worsening economic situation in Yemen.