Riyadh - A court in Saudi Arabia on Tuesday sentenced 15 people to death and several others to prison terms in a case involving an alleged Iranian spy cell, a sign of the continuing tension between the two Mideast powers.A Riyadh criminal court handed down its ruling to the 32 people who were charged, including 30 Saudis, one Iranian and one Afghan national. The defendants' names were not made public and Amnesty International criticised the proceedings as "a travesty of justice and a serious violation of human rights."There was no immediate reaction from Tehran.Saudi state media reported in February that those charged were accused of establishing a spy ring in collaboration with Iranian intelligence and providing Iran with highly sensitive information on the Saudi military.The reports said they also were charged with seeking to commit acts of sabotage against Saudi economic interests, inciting sectarian strife, recruiting others for espionage and participating in anti-government protests.Amnesty International said two of the 32 were acquitted. It said those charged were arrested between 2013 and 2014 without warrants, "were repeatedly interrogated without a lawyer" and were forced into signing confessions."Sentencing 15 people to death after a farcical trial which flouted basic fair trial standards is a slap in the face for justice," Samah Hadid, an Amnesty official, said in a statement.Tensions have been high between Shi'ite power Iran and Sunni-ruled Saudi Arabia since January, when the kingdom executed a prominent Shi'ite cleric along with 46 others.Saudi Arabia cut diplomatic relations to Iran after protesters stormed and ransacked two Saudi diplomatic posts in the Islamic Republic.