AAP said the BJP workers broke the doors and attacked the headquarters of the Delhi Jal Board.
Delhi Jal Board Vice-Chairman Raghav Chaddha's office at the agency headquarters was vandalised today, allegedly by BJP workers, over the party's support to the protesting farmers. "They (the BJP workers) said warn Kejriwal that he should stop taking the side of the farmers," Mr Chadha told reporters this evening. Soon after, Chief Minister Arvind Kejriwal tweeted a defiant message saying his party and government are "fully with the farmers till last breath".
"We are not afraid of such cowardly attacks. I appeal to all the workers not to be provoked by such attacks of the BJP and fully support the farmers," the Chief Minister said in a Hindi tweet.
In the evening, Delhi Police said they have detained 30 persons from the Jal Board office.
The ruling Aam Aadmi Party -- locked in a battle with the BJP over funds for the city's civic bodies -- earlier said the attack was a follow-up of the one at Deputy Chief Minister Manish Sisodia's home and the house arrest of Chief Minister Arvind Kejriwal.
The BJP workers were holding a demonstration since morning outside the Jal Board office under the leadership of Delhi BJP chief Adesh Gupta, AAP said in a Hindi statement.
"Around 12.30 in the afternoon, BJP workers broke the doors and attacked the headquarters of Jal Board and raised slogans against the honorable Chief Minister Arvind Kejriwal. The BJP workers have also damaged the office of Vice President Raghav Chadha," the statement added.
Mr Chadha tweeted a video of the damaged area, showing broken doors and flowerpots and glass strewn on the floor.
Earlier this month, AAP claimed that leaders and workers of the BJP had mobbed Chief Minister Arvind Kejriwal's home, vandalising property and breaking CCTV cameras.
Days before that, the party had released CCTV footage of the situation outside the home of Mr Sisodia following an attack by the BJP workers, allegedly in full view of the police.
The BJP had claimed it was in retaliation to a breach of privacy of their women workers. People from the Chief Minister's office were placing CCTV cameras where the women protesters were sleeping, the party said.
Over the last weeks, the BJP has been holding protests outside the homes and offices of AAP leaders, demanding payment of pending municipal funds. The party, which runs the municipal bodies, claims the Delhi government owes around Rs 13,000 crore.
AAP has alleged that a Rs 2,500 crore-fraud by the opposition party in the civic bodies.
After today's attack, Mr Sisodia said "Hooliganism is the second name of BJP". "The BJP people are now openly going into homes and offices and indulging in hooliganism," his tweet in Hindi read.