The Islamic State (IS) has claimed responsibility for a series of attacks at two mosques in Yemen that left at least 77 people dead on Friday.

The mosques were primarily used by the Shiite Muslim Houthi group in Sanaa, and over 121 people were wounded in the blasts.

The Badr mosque in southern Sanaa was targeted by a suicide bomber while worshippers were inside, and a second suicide bomber targeted the Shiites as they fled the carnage. A medical source reported that the mosque's imam, Al-Murtada bin Zayd al-Muhatwari, was among those killed.

The Al-Hashahush mosque in northern Sanaa was also hit by two suicide bombers, leaving hospitals in the area in urgent need of blood donations, according to Al-Massira television.

A source close to the militia in Yemen reported that another suicide bomber targeted a mosque in Saada, but only the attacker was killed. Security outside the mosque prevented the man from going inside.

In an online statement released Friday, a Yemeni branch of IS said that the five men were affiliated with their group, and called the attacks a "blessed operation" against the "dens of the Shiites." The involvement of IS in the mosque attacks have not been independently confirmed.

The extremists' statement was posted on the same website that alleged the group's involvement in the attack at a museum in Tunisia on Wednesday.

Two gunmen, Yassine Laabidi and Hatem Khachnaoui, descended on the National Bardo Museum in Tunis and shot and killed more than 21 people—many of them tourists. The men were killed by police during the ensuing gun battle.

In addition to IS, Uqba bin Nafa, a Tunisian group affiliated with Al-Qaeda, has claimed responsibility for the museum attack.