The attacks — at Christian religious buildings on a Sunday shortly before Christmas — caused shock and dismay.

Colorado Springs is a focal point of evangelical activity in the United States. New Life is a leading “megachurch” with more than 10,000 members and the city is also the headquarters for the influential Christian conservative group Focus on the Family.

“When innocent people are killed in a religious facility or a place of worship, we must voice a collective sense of outrage,” said Colorado Governor Bill Ritter.

Democratic Senator Ken Salazar of Colorado said, “It is incomprehensible that such atrocities could occur in places of faith and worship.”

In the Arvada shooting, a young man came to the door of the Youth With a Mission dormitory asking for a place to stay, the group said in a statement. When he was told he could not be accommodated there, he pulled out a handgun and opened fire. Two youth staffers were killed and two were wounded. They had been up late cleaning up after a Christmas party.

The mission is an international and interdenominational Christian organisation that trains young people to work as missionaries.

In Colorado Springs, staff at the New Life Church said they had tightened security after hearing about the Arvada shooting.

The roughly 7,000 people inside the building were swiftly evacuated to a downstairs basement after shooting started, pastor Brady Boyd told reporters.

The church was founded 20 years ago by pastor Ted Haggard who resigned in disgrace a year ago after admitting to sexually immoral conduct following a friendship with a male prostitute.