A suicide bomber detonated his explosives-laden car at the main gate of the heavily guarded police headquarters in southern Afghanistan's Helmand province Sunday, killing 12 police officers and a child and wounding a dozen others.

The blast in Lashkar Gah is the first major attack in the area since Afghan forces took over full security responsibility from NATO-led troops less than two weeks ago, in the first stage of a plan to have all of Afghanistan under the control of Afghan security forces by the end of 2014.

It also is the latest in a string of assaults that have included the assassination of several high-profile officials, including Afghan President Hamid Karzai's half-brother and the mayor of Kandahar city.

Taliban militants have claimed responsibility for the latest attack.

In other violence Sunday, NATO said five of its service members died in three separate incidents. A NATO statement said three troops died as a result of a non-battle related injury in western Afghanistan, another one was killed in a bomb blast in the east, and the fifth died in an insurgent attack in the south.

The blast in Helmand came as the top U.S. military officer met with commanders and troops in eastern Afghanistan, where members of the Taliban-allied Haqqani network are attacking U.S. forces.

Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, said the overall goal has been to make it much more difficult for the Haqqani network to penetrate directly what has previously been called the “jet stream” between Pakistan, right through Khost province into Kabul.

Mullen said Washington continues to press Islamabad to go after Haqqani militants and members of other groups that enjoy the safe havens in Pakistan.

But a senior NATO military official, speaking to reporters on condition of anonymity, acknowledged that there is only a minimal chance that the Haqqani threat can be eliminated.