The founder of several jihadist websites has pleaded guilty to three charges related to making online threats, including threatening the writers of the television show "South Park", according to the US Department of Justice.

Jesse Curtis Morton pleaded guilty in a US court to conspiring to solicit murder, making threatening communications and using the Internet to place others in fear. Morton, also known as Younus Abdullah Muhammed, founded Revolution Muslim, a group that used multiple websites and other Internet services to encourage Muslim radicals to commit violence against enemies of the religion, the DOJ said in court documents.

Morton faces a maximum penalty of five years in prison for each of the three charges when he is sentenced in May.

Morton founded Revolution Muslim in December 2007 and spread the group's pro-violence message on websites such as Revolutionmuslim.com, Revolutionmuslim.info and Revolution4muslim.com, according to court documents. The group also used Google Groups, YouTube, Facebook and other services to distribute its message, the DOJ said.

Morton's websites encouraged Muslims to support Osama bin Laden and groups including al-Qaeda and the Taliban, the DOJ said. Revolution Muslim's members posted messages in support of the terrorist attacks on the World Trade Centre, according to court documents.

"Jesse Morton operated Revolution Muslim to radicalise those who saw and heard his materials online and to incite them to engage in violence against those they believed to be enemies of Islam," said US Attorney Neil MacBride. "We may never know all of those who were inspired to engage in terrorism because of Revolution Muslim, but the string of recent terrorism cases with ties to Morton's organisation demonstrates the threat it posed to our national security."

Through his online forums, Morton conspired with blogger Zachary Chesser and others to solicit the murder of an artist tied to the Everybody Draw Mohammed Day movement in May 2010, including posting a magazine that included the artist in a hit list for violent extremists to take out, according to court documents. Morton posted online a speech of his asserting that "Islam's position is that those that insult the Prophet may be killed" and exhorting his listeners to fight the "disbelievers near you," the DOJ said.

Morton, in his plea, said he aided Chesser in taking repeated steps in April 2010 to encourage violent extremists to attack the writers of "South Park" for an episode that featured Muhammad in a bear suit. The two published information about the location of the residences of the show's writers and urged online readers to "pay them a visit," the DOJ said in court documents.

Morton and Chesser also published information explaining their religious justifications for killing those who insult or defame Muhammad.

Chesser was arrested on July 21, 2010, charged with providing material support to militant Muslim group Al-Shabaab and later also pleaded guilty to communicating threats and soliciting violent extremists to desensitise law enforcement. Four days after Chesser's arrest, Morton fled to Morocco, where he resided until his arrest on May 26, 2011.

Revolution Muslim was connected to several US and UK residents arrested on terrorism-related charges, the DOJ said.

Extremists connected to the group included Colleen LaRose, also known as Jihad Jane. LaRose was charged in March 2010 with several terrorism-related offenses, including plotting to kill Lars Vilks, a Swedish cartoonist who depicted Muhammad. LaRose subscribed to the group's YouTube accounts, the DOJ said.

Also connected to the group was Antonio Benjamin Martinez, who was arrested and charged with plotting to bomb a military recruiting station in December 2010. One month before his arrest, Martinez viewed multiple terror-training-camp video clips on a Revolution Muslim website, the DOJ said.

Rezwan Ferdaus was charged in September 2011 with plotting to attack the Pentagon and US Capitol using large, remote-controlled aircraft filled with plastic explosives. In February 2010, Ferdaus emailed Morton asking for counsel regarding his duties as a Muslim and whether martyrdom operations were proper practice. Morton replied that martyrdom operations must be judged by intention but can have "enormous benfits (sic) in a war of attrition".