A bomb likely hidden on a bus carrying high-ranking Yemeni air force personnel exploded Sunday in the capital, killing three people in a country fighting an al-Qaida affiliate, officials said.

The explosion in Sanaa came as al-Qaida’s Yemen branch posted a new video message saying killings in Muslim nations only act as a “stimulus” to draw more into fighting as militants.

The bombing wounded 23 people riding in the minibus, including five in critical condition with amputated arms or legs, said Col. Mahdi al-Aidarous, an air force spokesman. Among those wounded are 13 majors, lieutenant-colonels and colonels, the Defense Ministry said.

The colonel said the bus was heading to air force headquarters when the blast went off. He said it most likely originated from inside the vehicle. The official SABA news agency later quoted an air force statement as saying that the explosive was stuck under the bus.

Private television stations showed images of a damaged bus with blown-out windows and blood-stained doors. Security forces collected evidence at the scene.

No group immediately claimed responsibility for the attack, but Yemen’s government is battling militants linked to al-Qaida who regularly target the country’s military.

Al-Qaida in Arabian Peninsula, which is based in Yemen, recently posted a video message online delivered by a man identified as Sheik Harith al-Nadhari. In it, al-Nadhari talks about suspected U.S. drone strikes in Yemen and the recent killing of militants in Egypt in an Israeli drone strike.

“The killings for the sake of God … is a stimulus to us Muslims for jihad for the sake of God,” he said, according to a translation by the Washington-based SITE Intelligence Group, which monitors jihadist websites.

Al-Nadhari slammed America’s actions in Yemen, saying that drone strikes operate outside the law and punish for “mere suspicion.”

“Suspicion is enough a justification for America to kill whomever she wishes among the Muslims. She is exempted from questioning. Let Muslims be killed, then be said: suspected of association,” he said.

Amid a global alert about terrorism earlier this month, the U.S. evacuated its diplomatic staff from Yemen’s capital. The terror alert was followed by almost daily drone strikes in Yemen that killed at least 38 people, all suspected of being militants with al-Qaida.

Washington considers the Yemen-based al-Qaida to be the most dangerous offshoot of the terror network after it was linked to several attempted attacks on U.S. targets. Those attempts including the foiled Christmas Day 2009 bombing of an airliner over Detroit and the explosives-laden parcels intercepted the following year aboard cargo flights.

On Sunday, a criminal court began the trial of four al-Qaida members charged with planning an assassination attempt against President Abed Rabbo Mansour Hadi and the U.S. ambassador to Yemen.

According to Yemen state television, Judge Helal Hamed oversaw the proceedings. Prosecutors say the men belonged to al-Qaida between 2011 until early this year and plotted to kill the president with two explosives-laden cars. The men were accused also of planning to kill the U.S. ambassador and kidnap foreigners for ransom.