Brian Williams Cancels 'Leno' Appearance

Brian Williams will not be on The Jay Leno Show Oct. 28 as previously planned. The Nightly News anchor was scheduled to appear via remote from Afghanistan. But since Williams arrived there Oct. 26, violence has escalated.

On Monday, separate helicopter crashes in Afghanistan killed 14 Americans. On Tuesday, eight American soldiers were killed by roadside bombs, the biggest killer of U.S. soldiers fighting there. And early Wednesday morning, five U.N. staff members, including one American, were killed when Taliban militants attacked a heavily guarded private guesthouse in Kabul.

Williams' NBC News colleague David Gregory will pinch-hit.

Gregory will do the show's "10 @ 10" segment - a 10-question quiz and a favorite of politicos and news personalities. First Lady Michelle Obama, Health and Human Services Secretary Kathleen Sebelius, Rep. Barney Frank and MSNBC's Chris Matthews have been among the guests who have participated in 10 @ 10.