Describing as "most unfortunate" the incident of a protesting farmer hoisting a flag at the Red Fort, senior Congress leader Shashi Tharoor on Tuesday said he supported the farmers' protests from the start but cannot condone "lawlessness".

He asserted that on Republic Day no flag but the sacred tiranga should fly aloft the Red Fort.

"Most unfortunate. I have supported the farmers' protests from the start but I cannot condone lawlessness. And on #RepublicDay no flag but the sacred tiranga should fly aloft the Red Fort," the former Union minister said on Twitter, tagging a tweet which carried a video of the incident.

Wielding sticks and clubs and holding the tricolour and union flags, tens of thousands of farmers atop tractors broke barriers, clashed with police and entered the city from various points to lay siege to the Red Fort and climb the flagpole on Republic Day.

While farmer leaders, who have been spearheading the two-month protest at the national capital's border points to demand a repeal of the farm laws, disowned the protesters, one young man was seen hoisting a yellow triangular flag at the flagpole -- the centrepiece of the country's Independence Day celebrations.

The saffron flag hoisted by protesters from a staff at the iconic Red Fort during their tractor parade on Tuesday was the  'Nishan Sahib', a symbol of Sikh religion seen at all Gurdwara complexes.

The 'Nishan Sahib' is a triangular flag that is sacred to Sikhs. The emblem on the flag comprises of 'Khanda', a two-edged sword, Chakra, a disc, and two Kirpans that cross each other at the handles.

The other flag appeared to be of a farmer union.