Yemen's embattled president says suicide bombings that killed at least 142 people at Shi'ite Houthi mosques were aimed at dragging the country into "chaos, violence and internal fighting".
The Islamic State jihadist group claimed responsibility for Friday's attacks on two mosques in the capital Sanaa and the Houthi militia's northern stronghold of Saada.
President Abedrabbo Mansour Hadi has taken refuge in the southern city of Aden, having escaped house arrest in the Houthi-controlled capital last month.
In a letter to the families of the victims, which also included 351 wounded, he condemned the attacks as "terrorist, criminal and cowardly".
"Such heinous attacks could only be done by the enemies of life," who want to drag Yemen into "chaos, violence and internal fighting," said the letter released by his office late on Friday.
"Shi'ite extremism, represented by the armed Houthi militia, and Sunni extremism, represented by al-Qaeda, are two sides of the same coin, who do not wish good and stability for Yemen and its people," Hadi wrote.
The Houthis seized Sanaa in September, and have since tightened their grip on government installations, aided by forces loyal to former president Ali Abdullah Saleh.