"There was continuous machine gun fire and very loud, heavy explosions which were rattling the windows of houses across Sana'a," recalled Finn.

He says both sides are firing shells and anti-aircraft missiles at the other, ravaging part of the capital.

"The east of the capital has pretty much been evacuated. It's an area called Hasaba. It's a heavily, densely populated residential area which is now a ghost town," Finn said. "The houses are empty, the streets are filled with smashed up walls and concrete and bullet holes. It's essentially a battle zone in this neighborhood."

More residents were reported trying to leave the capital, after others fled during fighting between the two sides last week.

"What I'm seeing and hearing on the streets of Sana'a is sort of widespread panic and fear of what's coming in Yemen," said Finn.

The clashes in Sana'a and Zinjibar are but two of the fronts in the effort to force President Saleh from power. Witnesses in the southwestern city Taiz say more anti-government protesters were killed by troops Tuesday.

The government's deadly push to clear the city's central square began Sunday. The United Nations refugee agency says it has reports that more than 50 people have been killed in the crackdown in Taiz.

While the pressure on Saleh is clearly growing, whether his disparate opponents can, or even want to unite, is less apparent.

Tom Finn says the matter is dividing political protesters in Sana'a, who, inspired by uprisings in Tunisia and Egypt, have been seeking a democratic alternative to more than three decades of Saleh's authoritarian rule.