A court in Saudi Arabia on Monday jailed 13 defendants for up to 10 years on charges that included joining an Islamist group and fighting overseas.

The 13 were part of a larger group of 32 defendants and were convicted of "following the Takfiri doctrine", a term usually used to refer to al-Qaeda, the official SPA news agency said.

They were also convicted of charges including fighting abroad, supporting fighters financially, and helping "mislead" people travelling to conflict zones, SPA said.

Scores of Saudis are believed to be in the ranks of militant Islamist groups in areas of unrest across the Middle East, including Syria.

Some of the defendants were also convicted of possessing arms and undergoing weapons training.

One was also found guilty of "exploiting religious seminars to spread his deviant thoughts among his pupils", according to SPA.

In July 2011, a series of prosecutions began over alleged offences committed during the peak of al-Qaeda violence in the kingdom between 2003 and 2006.

In February, King Abdullah decreed jail terms of up to 20 years for citizens who take part in overseas conflicts, after the war in Syria attracted hundreds of Saudi fighters.

Saudi Arabia has keenly supported the formation of an international coalition to combat the rise of the Islamic State (IS) in Syria and Iraq, including its most senior religious cleric who recently branded the group “enemy number one of Islam.”

King Abdullah recently warned the group “will reach Europe in a month and America in another month” if it is not urgently confronted by “the broadest possible coalition of nations”. Domestically he has vowed not to “allow a handful of terrorists, using Islam for personal aims, to terrify Muslims or undermine our country and its inhabitants.”

Riyadh has faced accusations of tacitly funding the IS by turning a blind eye to private donations to them from within the kingdom, although the country's rulers have consistently refuted these accusations.

There does appear, however, to have been a swell of support for the IS among Saudi Arabia’s citizens. Ninety-five percent of mentions on the hashtags #TheAgeofTheISISConquest and #ABillionMuslimsForTheVictoryofTheISIS have emanated from the kingdom, according to Vocativ.

Pro-IS slogans have been graffitied on buildings across the country, which commentators have cited as evidence of strong domestic support for the group and a potential source of backlash should the rulers directly contribute to military attacks in Syria and Iraq.