RIYADH - A Saudi woman has been sentenced to six years in prison for "acts of sedition" including pledging allegiance to the Islamic State militant group, newspapers reported on Thursday.

A court in Riyadh issued the sentence against the unnamed 27-year-old on Wednesday, the Saudi Gazette said. But Al-Hayat daily reported that the judge decided to keep her in jail for only three years after she expressed "regret" for her "acts of sedition" and suspended the rest of the sentence.

She will however also be banned from travelling abroad for six years, it added. The woman was convicted of pledging allegiance to Abu Bakr al-Baghdadi, leader of the Islamic State group which has seized territory in Iraq and Syria.

She posted messages on Twitter supporting a deadly attack on security forces, and hung posters at a mosque and on utility poles to seek the release of a suspected militant, Saudi Gazette said. She also reportedly called for disobedience against the kingdom's rulers.

Saudi Arabia is part of the US-led coalition bombing IS in Iraq and Syria. Saudi political and religious leaders routinely denounce IS attacks - at home and abroad - as contrary to Islam.

Still, a report last year by the inter-governmental Financial Action Task Force said Saudis comprised the second largest nationality among "foreign terrorist fighters" with IS.