Yemen's embattled US-backed president pledged to step down more than a year early but refused to immediately resign on Tuesday, infuriating tens of thousands of demonstrators demanding his ouster.
The opposition said it would not accept President Ali Abdullah Saleh's offer to resign by year's end in response to nationwide anti-government protests, which have swelled dramatically since security forces opened fatally shot more than 40 demonstrators on Friday.
"The president's statements are just another political maneuver," said chief opposition spokesman Mohammed al-Sabri. "What was acceptable yesterday is not acceptable for us today."
The standoff pushed Yemen closer to open confrontation between the two sides, fueling Western fears that Saleh's 32-year-old regime could be replaced by chaos, or a leadership less likely to cooperate with US military operations against the local branch of al-Qa'ida.
Anger at Friday's shootings splintered Saleh's remaining support among the country's most powerful institutions, and influential clerics, tribal leaders and military commanders all began calling for his departure. Some of the country's most senior army officials declared their loyalty to the opposition on Monday.
Saleh responded with a concession, pledging in a meeting with senior officials, military commanders and tribal leaders on Monday evening that he would to step down by the end of the year. He tried to placate demonstrators by promising this month not to run again, or let his son replace him, when his term ends in September 2013.
A presidential spokesman, Ahmed al-Sufi, said Salah also pledged not to hand power to the military.
The president hardened his position on Tuesday, saying the defection of commanders including his chief military adviser, Maj. Gen. Ali Mohsen al-Ahmar, was a "mutiny and a coup against constitutional legitimacy."
"Any dissent within the military institution will negatively affect the whole nation," Saleh said in a nationally televised warning to a meeting of Yemen's Supreme Council of the Armed Forces. "The nation is far greater than the ambition of individuals who want to seize power."
Protesters massed by the tens of thousands Tuesday afternoon in the downtown Sanaa plaza they have dubbed "Taghyeer," or "Change" square. Crowds ululated, chanted and painted each other's faces in the red, white and black colors of the national flag. Conservative tribesmen bought their wives to the protest, and the women bought their children, all basking in a carnival atmosphere.
"The revolution has crossed its most difficult period," said activist Bashir al-Sid, smiling. "All that remains is the easy part."
Demonstrators began demanding Saleh's ouster more than a month ago, inspired by the wave of people power sweeping through the Middle East. His troops and loyalists have killed more than 80 demonstrators throughout Yemeni cities, according to an Associated Press tally of eyewitness, opposition and official accounts.
Al-Ahmar's defection was followed by a flurry of resignations by army commanders, ambassadors, lawmakers and provincial governors.
Al-Ahmar, commander of the army's powerful 1st Armored Division, deployed tanks and armored vehicles at the Defense Ministry, the TV building, the Central Bank and Taghyeer square, the demonstrator's epicenter.
In response, the Republican Guards, an elite force led by one of Saleh's sons, deployed troops backed by armor outside the presidential palace on the capital's southern outskirts.
Calling Al-Ahmar's defection "a turning point," Edmund J. Hull, US ambassador to Yemen from 2001 to 2004, said it showed "the military overall ... no longer ties its fate to that of the president."
"I'd say he's going sooner rather than later," Hull said.
The Qatar-based Al-Jazeera network said its Yemen offices were broken into late Monday by 20 armed men who used a mechanical drill to open the door before seizing its main satellite uplink equipment, computers, TV cameras and closed-circuit surveillance cameras.
Jazeera said it had asked the Yemeni interior ministry three days ago to protect the bureau and its staff the network's journalists were threatened. The ministry did not respond, the network said.
In a sign of the Obama administration's growing alarm over the regime's crackdown on demonstrators, State Department spokesman Mark Toner called for "a cessation of all violence against demonstrators," saying Saleh should "take the necessary steps to promote a meaningful dialogue that addresses the concerns of his people."
The 65-year-old president and his government have faced down many serious challenges in the past, often forging fragile alliances with restive tribes to extend power beyond the capital. Most recently, he has battled a seven-year armed rebellion in the north, a secessionist movement in the south and an al-Qaida offshoot that is of great concern to the US.
al-Qa'ida in the Arabian Peninsula, formed in 2009, has moved beyond regional aims and attacked the West, including sending a suicide bomber who tried to down a Detroit-bound airliner on Christmas Day with a bomb sewn into his underwear. The device failed to detonate properly.
Yemen is also home to US-born radical cleric Anwar al-Awlaki, who is believed to have offered inspiration to those attacking the US, including Army Maj. Nidal Hasan, who is accused of killing 13 people and wounding dozens in a 2009 shootout at Fort Hood, Texas.