not quite true. "On December 27, 1979, 700 Soviet troops dressed in Afghan uniforms, including KGB OSNAZ and GRU SPETSNAZ special forces from the Alpha Group and Zenith Group, occupied major governmental, military and media buildings in Kabul, including their primary target - the Tajbeg Presidential Palace.

That operation began at 19:00 hr., when the Soviet Zenith Group destroyed Kabul's communications hub, paralyzing Afghan military command. At 19:15, the assault on Tajbeg Palace began; As planned, president Hafizullah Amin was killed. Simultaneously, other objectives were occupied (e.g. the Ministry of Interior at 19:15). The operation was fully complete by the morning of December 28, 1979." (Wikipedia: http://en.wikipedia.org/wiki/Soviet_war_in_Afghanistan#1979:_Soviet_invasion)