Aparently it's a series of explosions near the embassy according to a 
follow-up.

TWP

http://news.bbc.co.uk/1/hi/world/middle_east/7620362.stm

Sky News apparently got a letter on 14 of September, also sent to UK and US 
embassies, demanding the release "of a certain prisoner" (Sky's words) or 
there would be attacks by car-based suicide bombers.  Sky say they get such 
letters periodically, but this one was very recent and quite accurate.

Four RPG's hit the US embassy, which is now on fire and there was around a 
20 minute gun battle with the attackers afterwards.

TWP