Al-Qaida's Yemeni branch on Wednesday claimed responsibility for last week's attack on French satirical newspaper Charlie Hebdo, which left 12 people dead and sparked a week of violence and massive anti-terror protests across the country.

Al-Qaida on the Arabian Peninsula, often considered the terror network's most active and dangerous branch, referred to the massacre as the "blessed battle of Paris" in an 11-minute web video, Washington Post reported. It said it had targeted Charlie Hebdo as "vengeance" for publishing images of the prophet Mohammed.

Nasr al-Ansi, the group's main ideological guide, said in the video that it "chose the target, laid the plan, financed the operation." He said Cherif and Said Kouachi, the brothers thought to have committed the killings, are "heroes of Islam."

Al-Qaida on the Arabian Peninsula, meanwhile, did not claim responsibility for Friday's siege at a kosher grocery store in Paris, in which four people were murdered, CNN reports. However, al-Ansi praised the attack, saying "it was a blessing from Allah."

U.S. intelligence services are "working as quickly as possible" to determine the video's authenticity, U.S. National Security Council spokesman Alistair Baskey said Wednesday.

"If genuine, this is only the latest example of the wanton brutality that is al Qaida's calling card and which it has visited upon innocents of all faiths," Baskey added.

Al-Ansi noted in his video posted on Twitter that orders for the Charlie Hebdo attack had come directly from Ayman al-Zawahri, al-Qaida's top leader and Osama bin Laden's successor, according to The Associated Press.

The Yemeni leader blamed not only Charlie Hebdo, but also the governments of France and the United States in his statement.

"It is France that has shared all of America's crimes," al-Ansi said. "It is France that has committed crimes in Mali and (North Africa). It is France that supports the annihilation of Muslims in Central Africa in the name of race cleansing."

Cherif and Said Kouachi both traveled to Yemen, and U.S. investigators say they think Cherif Kouachi left the country with as much as $20,000 from al-Qaida on the Arabian Peninsula, an unnamed U.S. official told CNN on Wednesday.