Street battles between government forces and armed tribesmen killed dozens of people and spread to new areas of Yemen's capital, forcing residents to cower in basements or brave gunfire to fetch bread and water.
Nearly four months of mass protests calling for President Ali Abdullah Saleh's ousting have exacerbated already dire poverty, shuttering businesses and forcing up prices of essential goods.
It is a trend that does not bode well for long-term stability in this gun-ridden corner of the Arabian Peninsula, home to an active al Qaida branch and other armed Islamist groups.
Yemen's mainly peaceful protests gave way to fighting last week between Mr Saleh's security forces and fighters loyal to the head of Yemen's most powerful tribal coalition, Sheikh Sadeq al-Ahmar.
At least 41 people were killed yesterday as clashes spread to new quarters of Sanaa.
Secretary of State Hillary Clinton said Mr Saleh's refusal to step down was prolonging the crisis.
"We cannot expect this conflict to end unless President Saleh and his government move out of the way to permit the opposition and civil society to begin a transition to political and economic reform," she told reporters in Washington.
President Barack Obama's Homeland Security and Counterterrorism adviser John Brennan was to travel to Saudi Arabia and the United Arab Emirates this week for talks on Yemen.
Fighting in the capital raged from early morning though midday, sending the crackle of gunfire and the booms of artillery strikes across the city.
The clashes spread from the Hassaba neighbourhood where tribesmen have seized more than a dozen government buildings, to new areas.