Police are investigating reports that several young adults wearing masks smashed windows at Mars Hill Church in Portland, Oregon, on Tuesday.

The attack on Pastor Mark Driscoll's church was believed to by members of a pro-gay group called "Angry Queers".

The damage to the historic stained-glass windows of the Portland church was estimated to be at several thousand dollars, Koinlocal6.com reported. KOIN said it had received an email from a group identified as "Angry Queers" accusing Mars Hill Church of being "notoriously anti-gay and anti-woman". The group allegedly targeted Pastor Driscoll, who has a strong stance against sexual relations outside of the confines of heterosexual marriage.

It is not known what exactly the group was trying to achieve in its alleged act of vandalism against the church, but a spokesperson for Mars Hill, Justin Dean, described the attack as "sad".

"Our pastors in Portland have made many efforts to build relationships with the homosexual community in Portland," Dean expressed. "Even though they chose to destroy our property and scare away people trying to worship Jesus, we wish them no harm."

Commenting on the issue of same-sex marriage, he said: "We believe there is a difference between marriage and civil union. 'Marriage' is a religious term and service for what happens, more so than a civil union. Politics has muddied the water for the conversation by making it a marriage issue. Politically it is a civil-union issue.

"At Mars Hill we believe that marriage (as a religious term) is between a man and a woman. We are not saying this to influence what political leaders decide, but to describe how we approach 'marriage' based on the Bible."

Driscoll appeared on "The View" in March to promote the book that he co-wrote with his wife, Grace, called Real Marriage: The Truth About Sex, Friendship, and Life Together. During the programme, the senior pastor was asked by co-host Joy Behar why he opposes homosexuality.

"Well, we are Bible-believing Christians," Driscoll explained. "We do hold to the teaching of Scripture and that is that sex is reserved for a married couple … a heterosexual married couple. So, even when we were dating and we were sexually active we were wrong. So, we don't want to say we are better or holier than anyone, but we were wrong as well and had to make some changes."