* Government presses offensive in south
* Security has deteriorated since former president unseated (Adds suicide bomb)
ADEN, Yemen, April 18 (Reuters) - Yemeni warplanes killed at least six militants linked to al Qaeda on Wednesday, the government said as it pressed ahead with an offensive against insurgents in the south.
Since the outbreak of anti-government protests that unseated former president Ali Abdullah Saleh, security has deteriorated in Yemen, particularly in the south, where the army is struggling to control Islamist fighters.
The defence ministry said it launched an air strike on a group of militants near the southern city of Lawdar, killing six.
Local residents told Reuters one other person was killed and two were injured when mortar rounds hit their houses. There was no independent confirmation of who launched the attacks.
In a separate incident, a suicide bomber on a motorcycle blew himself up at a military checkpoint in the southern port city of Aden, killing only himself, a security official said.
More than 200 people have died since the government of the impoverished Arabian Peninsula state stepped up attacks on the militants whom it accused of assaulting a military camp near Lawdar last week.
Exploiting weakened central government control, Islamist insurgents have taken control of a number of cities in the territory which is close to key shipping lanes in the Red Sea.
Yemen's new president Abd-Rabbu Mansour Hadi is facing challenges from Shi'ite Muslim rebels in the north and secessionists in the south. (Reporting by Mohammed Mukhashaf; Writing by Rania El Gamal; Editing by Michael Roddy)