In a statement issued from London, Altaf Hussain said that Sindh province is burning and the workers of the MQM are being treated like prisoners of war.
"Rangers have turned Sindh into an occupied province. Our workers are being treated like prisoners of war and the attitude of the Sindh Chief Minister Syed Qaim Ali Shah has been irresponsible," a press release on the party's website quoted Hussain as saying.
Hussain said he had called Zardari and Shah to discuss the role of Rangers in Sindh but was unable to establish contact with them despite several attempts.
He also said that Chief Minister Shah was unable to understand his call due to his old age.
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MQM, the single latest political party in Karachi and a dominant force in Sindh, has come under increasing pressure in recent months after Rangers stepped up their operations in Pakistan's most populous city and twice carried out raids on the MQM headquarters here in Federal B Area.
The Rangers claimed the collections were being carried out forcibly, a charge denied by MQM.
The MQM also faced heat after a recent BBC report claimed the party was receiving Indian government funds to create trouble in Pakistan.
India had rejected the report as "completely baseless", while MQM termed the report a part of media trial to weaken its political base in the country.