Tension brewed in parts of Mumbai and adjoining Thane districts today following yesterday's incident of stone pelting on Raj Thackeray's convoy by alleged NCP workers in Ahmednagar district, with MNS supporters attacking NCP office in Ambernath and calling a bandh.

Angry MNS workers burnt effigies of Deputy Chief Minister Ajit Pawar and blackened his posters in some parts of the city.

Incidents of stone throwing were also reported from city suburbs including Chembur, Kurla and Bandra, police said.

In Thane's Ambernath, MNS workers attacked NCP office and tried to enforce a bandh today.

However, NCP spokesman Mahesh Tapase, whose office was targeted in Ambernath around midnight, claimed his party workers foiled attempts by MNS men to enforce a bandh.

Minor clashes were reported between activists of the two parties but there was no official confirmation.

Some vehicles were also damaged by MNS supporters.

Suspected NCP workers had hurled stones at Thackeray's convoy at Bhingar in Ahmednagar district and waved black flags last evening when MNS boss had gone there for some party-related work.

NCP activists were furious at Thackeray's criticism of Pawar, nephew of party supremo Sharad Pawar, whom the MNS leader blamed for the severe drought in several parts of the state.

Thackeray had at a public meeting in Solapur recently attacked Pawar, who headed the water resources ministry between 1999 and 2009, for allegedly having failed to check water scarcity despite huge spendings on irrigation projects.

There have been allegations of a Rs 70,000 crore scam in the irrigation department, which has been with NCP since inception of Congress-NCP government in Maharashtra in 1999.

Meanwhile, MNS MLA Ram Kadam issued an open threat to NCP leaders and workers if they continued to target Thackeray.

"We know how to give tit for tat. We believe in replying in the language people choose to speak to us. They (NCP leaders) have forgotten that they have to move in Maharashtra.... Their homes are in Mumbai," he said while speaking to a TV news channel.

MNS leader in the legislative assembly Bala Nandgaonkar blamed NCP for the incidents.

"Raj saheb is on a state-wide tour (during which) he is bound to criticise the government and his opponents. Raj saheb targeted Ajit Pawar and he also responded. Such criticism is nothing new. However, throwing stones at our leader's convoy and women workers getting hurt in police lathi charge is simply not done," he told PTI.

On the attack by his partymen at NCP office in Ambernath, Nandgaonkar said MNS workers had merely reacted to the action of the ruling party. "It is upto them to stop. Our's was a reaction to their action," he said.

Shiv Sena spokesman and Rajya Sabha member Sanjay Raut said since the Home portfolio was with NCP, it was its job to prevent violence and maintain peace.

The ire against the stone-pelting incident was also witnessed in Nashik, where MNS activists burnt an effigy of State Deputy Chief Minister Ajit Pawar on the flyover bridge at the busy Mumbai-Agra national highway following which police rounded up 60-70 people.

However, there was no attack on any NCP office here, police said.

City NCP President Sharad Koshire strongly condemned the act and said they don't want to indulge in any kind of protests as it will disturb the law and order situation in the city.

Meanwhile, police have increased security around the house and farm of PWD minister Chhagan Bhujbal and NCP MP Sameer Bhujbal here and also the party office, situated on Nashik-Trimbakeshwar road.

Meanwhile, Mumbai Police today registered two FIRs against MNS workers, who have been charged with stone pelting, and vandalising the offices of NCP.

Six people were arrested in suburban Khar after they vandalised the local NCP office, police said.

In Antop Hill area of Central Mumbai, the police registered a case against four persons, all absconding, in connection with a stone pelting incident.

Police said some non-cognisable (NC) offences have also been lodged. In a non-cognisable offence police can neither file an FIR nor arrest anyone without court nod.

Police registered an NC case against MNS workers after they allegedly tore NCP posters in suburban Bandra.

In the Central suburb of Mulund, around a dozen people were detained for illegal assembly and sloganeering. Police officials said stone pelting was also reported from Vikroli area.

In adjoining Thane, police have stepped up security outside the offices of both NCP and MNS.

Last night, unidentified persons hurled stones at the NCP's main office in Thane located in Panchpakadi area.

In another incident, the police said an unsuccessful attempt was made by some persons, said to be MNS activists, to burn an effigy of Ajit Pawar in Kalyan.

A number of State Transport (ST) buses were damaged in stone pelting in Thane city, police said.

Speaking at a function, Rajan Gavand, Thane unit spokesperson of MNS, said his party will not tolerate incidents like attack on Raj Thackeray's convoy.