A rocket-propelled grenade (RPG) hit the building of the Yemeni national security headquarters in the capital Sanaa, which was followed with exchange of heavy gunfire on Thursday night, security sources said. The shootings continued till midnight, the sources told Xinhua on condition of anonymity, but gave no further details. Residents from the nearby neighborhood said heavy machine gunfire was heard and police forces cordoned off the whole area and closed all roads leading to the national security headquarters, which located in a densely populated area about 7 km northeast of the defense ministry. No casualties have been reported yet. Earlier in the day, around 12 al-Qaida gunmen stormed a military hospital inside the complex of the Yemeni defense ministry in Sanaa with two car bombs, killing at least 52 people and injuring 167 others, according to the supreme security committee. The committee said the victims included two German aid workers, two Vietnamese doctors, two Filipina nurses and an Indian nurse. It blamed the attacks on the al-Qaida in the Arabian Peninsula ( AQAP) that is based in the country's southern regions. Residents said gunfire and explosions are still heard near the defense ministry compound at late night. Yemen has undergoing a transitional political period after a year of mass protests that eased former President Ali Abdullah Saleh from power in 2012. Violence has since escalated in the impoverished Arab country as the government blamed most of attacks on the al-Qaida group that has been considered the most dangerous regional branch in the Middle East. President Abd-Rabbu Mansour Hadi's administration has intensified efforts to crack down on the militants, including drone strikes as part of a U.S.-backed anti-terrorism campaign.