Two foreign activists detained after a Gaza-bound flotilla was intercepted by Israeli forces are facing psychological abuse, death threats and harsh prison conditions, according to a rights group representing them.

Spanish national Saif Abu Keshek and Brazilian Thiago Avila were brought to Israel for questioning after their vessel was stopped off the coast of Greece. An Israeli court has extended their detention, while authorities consider further legal action.

Lawyers who visited the men say they are being held in total isolation under constant bright lighting, exposed to extreme cold, and blindfolded whenever moved outside their cells, including during medical visits. Avila reportedly endured interrogations lasting up to eight hours and was allegedly threatened with being 'killed' or spending '100 years in jail.' Both men are on a hunger strike.

Israeli authorities deny claims of torture or physical abuse and accuse the activists of offenses including assisting the enemy during wartime and ties to the Popular Conference for Palestinians Abroad, which Israel links to Hamas. The flotilla sought to deliver humanitarian aid to Gaza, which has been under an Israeli blockade since 2007 amid ongoing shortages of critical supplies.