A clash between Samajwadi Party activists and the police, who resorted to firing in the air in Lucknow on Friday, has heightened political tensions in Uttar Pradesh.

The clash followed denial of permission by the Mayawati government to a public demonstration by the Samajwadi Party youth wing. "Our aim was to highlight the high-handedness of the Mayawati government through a peaceful march from our party office to the district collectorate where we would have staged a symbolic demonstration," party Member of Parliament and national chief of party's youth wing Akhilesh Singh Yadav said.

His father and Samajwadi Party president Mulayam Singh Yadav termed the lathi charge and by the police as a reflection of the highly "undemocratic and high-handedness of the chief minister."

The clash took place just outside the SP state headquarters, leaving at least a dozen, including a few policemen injured, and hospitalised.

The administration had virtually sealed off all entry points to the state capital to prevent entry of vehicles carrying Samajwadi Party activists from other parts of the state. Heavy police deployments were made from early morning at all strategic points, including the main shopping centres and downtown Hazratganj.

The administration had ordered closure of educational institutions in the proximity of the Samajwadi Party office.

The began around 1100 hours IST, when a heavy armed police contingent prevented Samajwadi Party activists from stepping out of the party headquarters from where they had planned their march. After a heated exchange, SP activists started pelting stones at the cops, provoking pitched battles between the two for the next hour and a half.

Both the Provincial Armed Constabulary and Rapid Action Force men were seen retaliating with a volley of stones inside the locked gates of the SP office, while several teargas shells were burst to keep other SP supporters at bay.

SP chief Mulayam Singh Yadav accompanied by party general secretary Amar Singh addressed the party workers inside the party office compound.

Terming the Mayawati administration's action as "highly undemocratic", Amar Singh said, "The fact that she used such brute force against our partymen clearly reflects her own defeat and a scoring point for us." Flaying her for "gross misuse of POTA", he declared amid applause, "Once Samajwadi Party comes to power, we will see that Mayawati pays for her misdeeds by getting her booked under POTA."

Later, a large number of SP workers were arrested as they came out of the party office.

Defending the arrests, Lucknow Deputy Inspector General A K D Dwivedi said, "The demonstration had been banned by the administration, so whatever SP workers did was illegal and unlawful."