A suicide bombing killed at least 20 police cadets in Yemen's capital of Sanaa on Wednesday, just five days after the terrorist group sent warning messages to intelligence services that an attack would strike police institutions in days.

The deadly bombing was the second in less than two months in Sanaa, after the deadliest-ever attack on a military parade rehearsal in al-Sabeen Square in May, which killed about 100 central security forces in a highly-guarded square adjacent to the presidential palace.

"It's an urgent message to chiefs of the Yemeni intelligence services, the political security agency and the national security that we will carry out another sophisticated operation against police forces in Sanaa in days," an al-Qaida spokesman identified himself as Abu Hajar al-Hadramy said in an audio tape carried by al-Qaida media Al-Malahim Foundation on July 6.

Wednesday's attack, which occurred in front of the police academy in downtown Sanaa while the cadets were leaving after classes finished, left at least 20 killed and dozens of others injured, according to security sources.

"It's al-Qaida ... it's our job now to clean Sanaa from their threats and reaching the house of the suicide bomber," an officer told Xinhua anonymously, adding that "a foreign interest could be targeted next time according to intelligence information."

Outside the southern gate of the police academy, which is about one kilometer north of the presidential palace and al-Sabeen Square, hundreds of people gathered there after hearing a powerful explosion.

Blood was splattered everywhere as the scene was cordoned off by police investigators, after ambulances transported the dead and injured cadets to nearby hospitals. Police sources said U.S. counter-terrorism experts took part in the investigations.

"President (Abd-Rabbu Mansour) Hadi's intelligence agencies need to take more precautionary measures to prevent further terrorist attacks," said Ahmed Tahir, a local resident.

Another passerby said "it's a very sad moment ... the terrorist attack today remind us of May 21 deadly attack in al-Sabeen Square. "

Police sources said that those cadets were killed when a suicide bomber jumped to them while they were leaving the academy for the weekend and about 20 others were wounded, five of them were in critical condition.

The Yemeni sharing-power government and opposition parties condemned the attack, requesting the interior ministry and security authorities to quickly capture terrorist perpetrators and bring them to justice.

The country's high security commission vowed to pursue al-Qaida cells in Sanaa and other provinces and "strike them with an iron hand," in a statement carried by the defense ministry's website.

Shortly after the bombing attack, the al-Qaida in the Arabian Peninsula (AQAP) claimed responsibility in a text message obtained by Xinhua and vowed to launch further attacks.

Despite the U.S.-backed military offensive that attempting to drive the terrorists out of their strongholds in the country's southern provinces of Abyan and Shabwa, Wednesday's suicide attack showed that the AQAP still poses severe threats after it retreated from cities in the southern provinces of Abyan and Shabwa.

In the warning message received by the security authorities in Sanaa last week, the AQAP also vowed to launch more attacks in Sanaa and threatened to retake Abyan and its neighboring regions. The Yemeni army announced in early June that they recaptured major cities in Abyan and declared that the military operation ended in victory.

VietNamNet/Xinhuanet