A police officer on patrol at 4am spotted the hate messages painted on the front wall of the Islamic Centre of Cypress, said Sergeant Tom Bruce. The paint was still wet, he said.

Rusty Kennedy, executive director of the Orange County Human Relations Commission, said the graffiti was about 4 feet or 5 feet tall (more than 1 meter tall) and spread over up to 30 feet (10 meters) of the wall.

In an e-mail to Muslim-American community leaders, Mr Kennedy reported that the graffiti read in part: 'We will kill you all' and 'US military is going to kill you all.' Police said there were no witnesses and the incident was not caught on surveillance video.

The graffiti was quickly removed or covered over. By afternoon, a patch of fresh white paint covered a large area on the single-story, stucco building, which faces a Korean Lutheran church and strip mall on a busy residential street.

A handful of men gathered in the mosque's office and several prayed quietly.

Mr Kennedy said it was likely the graffiti was prompted by Obama's outreach to the Middle East. The vandalism occurred about an hour after Obama's speech at Cairo University in Egypt aired live on the West Coast.

'I think that in the realm of hate crime you see there is often a reactionary element to it, so the Obama initiative... may very well have been what triggered this hate crime,' he said.

Ahmed Mehtar, the mosque's imam, said he wasn't sure of the link. 'We don't know the reason behind what was done,' he said. 'It is upsetting but since we don't know why it happened, it's hard to say.'

Shakeel Syed, executive director of the Islamic Shura Council of Southern California, said there is a small Muslim community in Cypress. The mosque is one of the smaller ones in Orange County, with anywhere from 50 to several hundred attendees depending on the day and service, Mr Syed said.

Mr Kennedy said there were 79 hate crimes in Orange County in 2008, down slightly from 82 the previous year. -- AP