New Delhi, Jan 29: Delhi Police Crime Branch has issued notice to six farmer unions to join the probe into the unprecedented rampage by farmers during their rally on Republic Day that left at least one person dead and several injured.

They have been summoned to join the investigation and record their version before the Crime Branch. Of the 33 FIRs registered in connection with the January 26 violence, nine will be investigated by the Crime Branch.

Lookout circulars have already been issued against 44 protesters and farmer leaders.

Police have also written to farmer leaders asking for details about their organisation's role in the clashes that lasted for hours and culminated with the hooligans running amok and vandalising inside the Red Fort.

The Delhi Police is also probing the role of foreign organisations and individuals in the violence that took place on the Republic Day, thus widening the probe ambit.

The Special Cell of the Delhi Police is probing the role of foreign hands -- individuals based in India and outside as well as organisations.

After slapping sections of rioting, criminals conspiracy and attempt to murder, the Delhi Police has pressed more serious sections like UAPA (Unlawful Activities Prevention Act) and sedition charges on the protesters found involved in the violent protests three days back.