ADEN, Yemen, Nov. 5 (Xinhua) -- Fierce armed clashes continued Sunday between Yemeni security forces and the Islamic State (IS) militants at Aden's security HQ, killing 21 people, a military source said.
A military source based in Aden's neighborhood of KhorMaksar said that the security forces supported by anti-terror units attempted to raid the building of the Criminal Investigations Department (CID), but a huge explosion occurred.
He said that many officers and policewomen are besieged inside the CID building where a number of IS militants are hiding since Sunday morning.
One of the Islamic State militants blew up himself as the security forces attempted to raid and cleanse other rooms of the CID building from the terrorists, he added.
Additional security soldiers and hostages were killed in the suicide bombing that happened around 5:30 p.m. local time, according to the sources.
Residents confirmed to Xinhua saying that "the clashes and explosions are still ranging out across the area. Elite soldiers are trying to kick the terrorists out of the security buildings."
"The security soldiers are now in full control of the area but there is a real difficulty in terms of freeing the hostages inside the CID building," a police officer near the scene said.
"Unknown number of terrorists took positions inside the building and threatened to blow themselves up if any security soldiers approached or raided the building," the police source added.
Meanwhile, a medical official told Xinhua that "today's three explosions and clashes resulted in killing 21 soldiers and injuring more than 30 others."
Earlier in the day, the Islamic State (IS) group claimed responsibility for a suicide bomb attack against the Criminal Investigations Department (CID) and the security headquarters in Aden.
"One of the group's jihadist members carried out the operation and detonated his explosives-loaded vehicle at the main gate of the Criminal Investigation Department in Aden," the group said in a brief statement, which its authenticity could not be independently verified.
The extremist group claimed that the "suicide operation that struck the main gate of the CID killed 30 soldiers and followed by another armed attack that resulted in killing 20 others."
The southern port city of Aden is considered as Yemen's temporary capital and the Saudi-backed Yemeni government based itself there since 2015.
Militants of the Yemen-based al-Qaida branch and the Islamic State group (IS) are more active in the country's southern part and Yemeni armed forces supported by the UAE started waging large offensives against some hideouts there.
The al-Qaida and Islamic State-linked terrorists took advantage of the security vacuum and ongoing civil war to expand their influence and seize more territories in Yemen.
Security in Yemen has further deteriorated since March 2015, when war broke out between the Shiite Houthi group, supported by former President Ali Abdullah Saleh, and government forces backed by a Saudi-led Arab coalition.
UN statistics show more than 10,000 people, most of them civilians, have been killed since the coalition intervened in the Yemeni civil war that also displaced around three million.
The impoverished Arab country is also suffering the world's largest cholera epidemic since April, with about 5,000 cases reported every day.