An Omani court jailed a prominent activist for three years on Sunday for a range of offences including undermining the state, a charge a newspaper said was related to an open letter to U.S. President Barack Obama about human rights in the country. Western-allied Oman, which experienced Arab Spring protests in 2011, has tried to clamp down on public dissent, arresting rights activists who criticise authorities on social media. Omani online newspaper Mowatin www.mowati**man.net said the charge of undermining the state stemmed from a 2013 open letter to Obama in which Jadad had expressed "dismay" over U.S. policies regarding human rights in the Gulf region. "We expect the United States, being a superpower, to always stand by the people and to support the principles of democracy and human rights," he wrote.