SANAA (AP) ― Yemeni government forces on Wednesday fired mortars at tens of thousands of mourners at funerals held for protesters killed in clashes and attacked an opposition base, shattering a cease-fire negotiated a day earlier to end the Arab nation’s latest bout of deadly violence. The two attacks killed 16 people.

The mourners were gathered for funeral prayers for anti-government protesters killed in a deadly, three-day government crackdown in which the death toll topped 80 ― a sudden spike in violence explained by protesters’ impatience with their longtime president, Ali Abdullah Saleh, who they say is dragging his feet instead of signing a deal to step down. Nine people were killed.

Also in Sanaa, the headquarters of the renegade 1st Armored Division came under heavy shelling from government forces killing seven, including two civilians, and injuring 10 others.

The officials said the shelling targeted a part of Change Square, where protesters have camped out since February to demand the ouster of Saleh, in power since 1978. Snipers on rooftops hunted down protesters in Sanaa main road of al-Zubairi, according to Tarek Noamani, a doctor at the square field hospital.

The officials spoke on condition of anonymity because they were not authorized to speak to reporters.

The International Committee of the Red Cross expressed concern about “unprecedented level of violence.” It said in a statement that at a main hospital, a team of the Yemen Red Crescent society was barred from access to injured people and that their team was “threatened and assaulted.” In some cases, they had equipment confiscated, the statement said.

The 1st Armored Division, one of Yemen’s most combat tested military outfits, mutinied in March to join the opposition. It is led by Saleh’s one-time confidant and war veteran Maj. Gen. Ali Mohsen al-Ahmar.

The targeting of the division’s headquarters is the latest indication that the fight over control of the Yemeni capital will primarily pit the rebel unit against the elite Republican Guards, led by Ali’s son and one-time heir apparent Ahmed.

Both sides claim about 20,000 fighters inside the capital, but the Guards have superior weaponry. Military experts say the final showdown between them would be won by the side that shows better urban warfare techniques.

The Al-Ahmar office issued a statement holding government forces responsible for “breaching the cease-fire.”

“This is an attempt to explode the situation militarily and to impose a situation that triggers confrontation,” the statement said, calling for international mediators to “discipline this gang and stop its barbaric actions.”

Gulf and U.N. mediators appear to have given up on persuading Yemen’s opposition and the government to talk about their transition plan, which has been on the table for months. It would allow Saleh to resign in exchange for immunity from prosecution. Saleh has come close to signing several times, only to pull back at the last minute.

Saleh is still in Saudi Arabia, where he went for treatment after suffering severe wounds in an attack on his Sanaa compound in June. Last week, he mandated his vice president to negotiate over the plan proposed by the Gulf Cooperation Council, a loose six-nation alliance of energy-rich nations, and backed by the United States.

The opposition rejected his move as more stalling.

Abdullatif bin Rashid al-Zayani, the GCC’s general-secretary, abruptly left Yemen Wednesday, according to a Yemeni government official. Al-Zayani’s departure came shortly after meeting with Vice President Abed Rabbo Mansour Hadi.

The official spoke on condition of anonymity because he was not authorized to speak to the press.

The resumption of violence on Wednesday followed a brief lull that allowed Sanaa residents to venture out from their homes morning to buy food and other supplies. Many hurried back home as an outburst of heavy gunfire rang out from an area close to the residence of the vice president.

Yemen’s turmoil began in February as the unrest spreading throughout the Arab world set off largely peaceful protests in the deeply impoverished and unstable corner of the Arabian Peninsula that is also home to an al-Qaida offshoot blamed for several nearly successful attempts to attack the United States.

The government has responded with a heavy crackdown, with hundreds killed and thousands wounded.