The father of a convicted bank robber who's on hunger strike to protest his barring from university says a meeting with Greek Prime Minister Antonis Samaras has failed to end the standoff, which has triggered violent protests.

Giorgos Romanos says his 21-year-old son Nikos is in "critical" condition after the four-week hunger strike, and is determined to persist.

While in prison awaiting trial for the armed robbery, Nikos Romanos successfully passed university entry exams to study business administration in Athens. Greek law allows convicts to attend classes on a case-per-case basis, but Romanos' application was rejected after his conviction.

The government has offered distance learning, which Romanos rejects.

Greece's justice minister also attended Monday's meeting between Samaras and Giorgos Romanos, who calls his son a "political prisoner."