According to police, the first one to be stopped at the security check point at Jashn-e-Rekhta event at Indira Gandhi National Centre for Arts, was a Delhi University student, who claimed to be the member of Left student group SFI.
Several posters, containing slogans of democracy, equality and justice, were recovered from him.
Soon, six others from the same group were detained and taken to Parliament Street police station.
Three of them were also carrying tambourines.
While six of them were released late afternoon, the youth who was stopped first, identified as Umar Shaqib, was released in the evening.
"It was a case of preventive detention. The youths could not be allowed to enter the concerned premises with the articles they were found to be carrying," DCP (New Delhi) Jatin Narwal said.