By Dan Merica, CNN

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Washington (CNN) – A Lutheran pastor has apologized after being chastised by his denomination's leader for offering a prayer at an interfaith vigil for the victims of the school shooting in Newtown, Connecticut.

Pastor Rob Morris, who leads the Christ the King Lutheran Church in Newtown, violated the Lutheran Church-Missouri Synod's rule against taking part in joint worship services, said the synod's president, Pastor Matthew C. Harrison.

Participation could be seen as endorsing "false teaching" because some among the diverse group of religious leaders at the vigil hold beliefs different from those of synod.

The vigil, which was attended by President Barack Obama, was a high-profile part of the healing process for the families of the 20 children and six adults killed at Sandy Hook Elementary School on December 14.

One of the victims of the shooting was a young congregant of Morris' church.

In an open letter posted online, Harrison wrote that because of "the presence of prayers and religious readings" and the fact that "other clergy were vested for their participation," the event was a "joint worship with other religions."

"I could draw no conclusion other than that this was a step beyond the bounds of practice allowed by the Scriptures," Harrison wrote. "There is sometimes a real tension between wanting to bear witness to Christ and at the same time avoiding situations which may give the impression that our differences with respect to who God is, who Jesus is, how he deals with us, and how we get to heaven, really don't matter in the end."

Harrison then "asked Pastor Morris to apologize for taking part in the service" because he "violated the limits set by Scripture regarding joint worship" and "gave offense" to the Lutheran leadership.

A day after Harrison's letter was posted, Morris apologized in another open letter.

"To those who believe that I have endorsed false teaching, I assure you that was not my intent, and I give you my unreserved apologies," Morris wrote in a letter to the Lutheran leadership. "I apologize where I have caused offense by pushing Christian freedom too far, and I request you charitably receive my apology."

In the same letter, however, Morris defends his decision to participate, writing that he believed his participation was "not an act of joint worship, but an act of community chaplaincy."

"Those who have followed the news reports are aware that this event is not quite like anything that has happened before," Morris wrote. "I believe (and I fervently pray) that my ministry will never involve a parallel situation to the one that faced my congregation and community that weekend."

According to the Lutheran Church-Missouri Synod, participating in joint worship events, particularly with religions that "reject Jesus," is forbidden and violated the synod's constitution. In his letter, Harrison cited Romans 16:17 as the justification for this rule.

"I urge you, brothers, to watch out for those who cause divisions and put obstacles in your way that are contrary to the teaching you have learned," the passage reads. "Keep away from them."

Morris is not the first Lutheran pastor to be reprimanded for participating in an interfaith event. After the terrorist attacks of September 11, 2011, a New York pastor was suspended for participating in a similar interfaith event memorializing those killed in attack on the World Trade Center.