A gunman said "I don't like your politics" before opening fire on a Christian lobby group's security guard in Washington DC, says the FBI.

Floyd Lee Corkins, 28, also allegedly had a bag full of sandwiches from a fast-food chain that was at the centre of a row over gay marriage.

The suspect had worked at a gay community centre.

The attack happened on Wednesday at the Family Research Council, which opposes gay marriage and abortion.

Security guard Leonardo Johnson, 46, is recovering in hospital from a wound to the arm. He and other guards restrained the gunman after the shot rang out.

The shooting drew swift condemnation from President Barack Obama and Republican challenger Mitt Romney, as well as a range of advocacy groups.

We're not backing up, we're not shutting up Tony Perkins, Family Research Council

Mr Corkins, from the US state of Virginia, faces a charge of assault with intent to kill, and a count of bringing a firearm across state lines.

He used a 9mm pistol that was legally bought and owned, according to the authorities.

His parents told FBI agents that their son has "strong opinions with respect to those he believes do not treat homosexuals in a fair manner", the complaint says.

In the suspect's backpack, police found a box of ammunition and 15 sandwiches from the fast-food chain Chick-fil-A.

The Family Research Council's president publicly supported the restaurant business after its boss said in July he backed the "biblical definition of a family", a remark that triggered protests.

The lobby group's leader, Tony Perkins, said the attack would not deter his organisation.

"We're not going anywhere. We're not backing up, we're not shutting up. We have been called to speak the truth," Mr Perkins said, reports AP news agency.