MANAMA, Bahrain — ­Bahrain’s highest court Monday upheld jail terms for 20 ­opposition figures — including eight sentenced to life — for alleged plots to ‘‘overthrow’’ the state. The decision is likely to touch off more protests in the Gulf nation and renew criticism from its Western ­allies.

The group includes a rights activist who staged a 110-day hunger strike last year to protest the verdicts, which critics have denounced as part of attempts to crush an Arab Spring-inspired uprising that began nearly two years ago in the strategic island kingdom.

Authorities in Bahrain — which is home to the US Navy’s Fifth Fleet — accuse Iran of ­encouraging the Shi’ite-led ­protests as a way to undermine Bahrain’s pro-Western leadership and gain a key foothold on the doorstep of rival Saudi ­Arabia.

Tehran has sharply ­criticized Bahrain’s crackdowns but denies it has any direct role with the opposition.

Bahrain’s majority Shi’ites, who have led sporadic unrest in past decades, say they face systematic discrimination at the hands of the Sunni monarchy. Bahrain’s rulers have offered some reforms, including giving more powers to the elected Parliament, but protest leaders say they fall short of demands for a role in key government affairs.

More than 55 people have died in the unrest since February 2011 and many opposition leaders and activists have been arrested, including the group of 20 charged with ‘‘plotting to overthrow’’ the ruling system by leading the protests.

Defense lawyer Jalil al-Aradi said the high court refused to reconsider the sentences or convictions.