Kandahar: The recent spike in spectacular violence rocking southern Afghanistan has been expected, but it's not clear yet how the attacks will affect the area's fragile governments, the top US military officer said as he arrived in the embattled region.

Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, told reporters travelling with him on Friday that he plans to talk to Afghan leaders during his visit about the surge in dramatic attacks and political assassinations in the south, and said U.S. officials are working hard to advise them how to improve their own security.

Mullen's unannounced trip to the region with late night talk show host Jon Stewart and others in tow to entertain the troops comes on the heels of a spate of bombings on Thursday in the southern province of Uruzgan that killed at least 19 people, and just days after Kandahar's mayor was assassinated by a suicide bomber. The mayor was the third southern Afghan leader to be killed in the last three weeks.

Mullen's visit, his 15th to Afghanistan, comes at a critical political and military time, as he looks to assess the ability of the Afghan security forces to weather the violence and lay a path for their future.

Within months U.S. troops will begin their slow but deliberate withdrawal from Afghanistan, a process that is coming under more pressure from a Congress determined to slash spending, including on the Afghanistan and Iraq wars.

There have been expectations, Mullen said, "that there are going to be these kinds of spikes, in particular these spectacular assassinations. There are some who believe this is all they can do, given the challenges that the Taliban have faced over the course of the last couple of seasons."

The Taliban have claimed responsibility for the attacks, in a clear bid to regain territory they lost over the past fall and winter as coalition forces pressed into insurgent strongholds in the south.

There are persistent fears, however, that the escalating violence will jeopardise coalition gains, erode citizens' confidence in the Afghan government's ability to protect its own people, and undercut U.S. efforts to turn security over to the Afghans.