A diplomatic source told me it was a sophisticated attack involving two car bombs and three suicide bombers with explosives belts, one of whom blew himself up just meters away from the embassy's main gate.

The entire attack, he said, lasted 15 minutes and left 16 dead -- five Yemeni security forces, one U.S. embassy Yemeni guard who was shot by the assailants when he tried to bar the first vehicle from entering the embassy parking lot, six of the attackers and four civilians, including an 18-year-old Yemeni-American woman from Bufallo, New York.

Yemeni government security guards outside the embassy told me the attack was by "cowards" who kill innocent people. We saw several people who appeared to be U.S. investigators surveying and photographing the damage.

We were allowed into the area by Yemeni security officials who didn't coordinate with the Americans. One of the investigators exclaimed to another (and I overheard) "Who the f***k allowed CNN in here?"

Shortly afterwards a security officer from the embassy told us to leave the area directly in front of the embassy because we were endangering the evidence, although dozens of Yemeni troops were milling around the area.

She told the CNN crew to go to the other side of the barrier in front of the embassy, "up against the wall" on he other side of the street.

The atmosphere in sanaa is calm, streets are quiet and of course it's Ramadan, so it's quiet on top of quiet. That's all for now.

-- From CNN Correspondent Ben Wedeman