Tensions between Yemeni President Ali Abdullah Saleh and an influential dissident general escalated Saturday amid fresh assaults that killed at least 40 people and injured scores. The mounting violence came a day after Saleh abruptly returned from Saudi Arabia after nearly four months and called for a cease-fire and a return to negotiations to solve Yemen’s crisis.

In a sternly worded statement, Gen. Ali Mohsen al-Ahmar, whose forces control many parts of the capital, warned that Saleh was propelling the country toward civil war and urged the United States, Yemen’s Persian Gulf neighbors and the international community to stop him.

Mohsen called Saleh “ignorant and bloodthirsty” and compared him to the Roman emperor Nero, burning down his own city.

“With his return, Yemen is experiencing sweeping chaos, and the harbingers of a crushing civil war which this ignorant man is determined to ignite,” he said in the statement.

He urged the international community to “deter him, stop his irresponsible actions where he intends to ignite a civil war that would bring down the whole country and have repercussions on the whole region and on world peace.”

Mohsen’s statement — his strongest public rebuke of Saleh since Yemen’s populist uprising began in February — came shortly after mortar shells fell on the main base of his 1st Armored Division, killing 11 troops and injuring more than 100, according to Mohsen’s aides. Suspicion immediately fell on forces loyal to Saleh who have battled Mohsen’s troops over the past six days in Sanaa.

Saleh spokesman Ahmed al-Sufi denied that government forces were behind the assault and said it was a ploy by the general to target the president.

“Ali Mohsen condemns the attacks that he himself makes,” Sufi said.

In another part of the capital, government forces attacked Change Square — a sprawling camp where activists have staged an eight-month sit-in to end Saleh’s 33-year reign — with mortar shells and heavy gunfire in Saturday’s pre-dawn darkness. Rooftop snipers shot at protesters and Mohsen’s soldiers protecting the square. As many as 17 were killed and scores injured, according to medics at a makeshift hospital inside the square. Other medics said the toll was higher. Hundreds more were forced to flee.

“Seventy percent of the dead and injured were shot by snipers,” said Mohammed al-Qubati, a medic who manages the makeshift hospital.

In the capital’s Hassabah district, Saleh’s forces clashed with tribesmen loyal to the Ahmar family, killing at least 18 tribal fighters, the family said. The Ahmars, who are not related to Mohsen, lead Hashid, Yemen’s most powerful tribal confederation.

Interior Minister Mouthar al-Masri told reporters Saturday that eight government soldiers had been killed and dozens injured, although he did not specify when or where those casualties took place. He also denied any government hand in the attack on Change Square, describing it as the work of “extremists.”

Once Saleh’s right-hand man, Mohsen defected in March after snipers loyal to Saleh killed dozens of protesters. His soldiers have vowed to protect the demonstrators from attacks by Saleh’s forces and end Saleh’s rule.

Saleh returned from Saudi Arabia, where he received treatment for severe injuries suffered in June in an attack on his presidential compound. Many Yemenis fear that his return will inflame violence, and Saturday’s attacks appeared to be an attempt to retaliate against his rivals. But such tactics could propel Yemen toward civil war.

In his statement, Mohsen warned that his troops were in a position to remove Saleh and to “restore the power usurped by this gang,” referring to Saleh’s family. But he said that Yemen’s peaceful uprising would continue to push for the fall of the regime.