Pakistan's top court on Wednesday summoned the new prime minister to appear later this month to face possible contempt charges, the clearest sign yet it could dismiss a second premier in a showdown over corruption cases.

The Supreme Court - which disqualified and convicted prime minister Yousuf Raza Gilani over the issue - summoned his successor Raja Pervez Ashraf on Aug 27 for ignoring a request to ask Swiss authorities to reopen cases against the president.

It is the latest episode in a two-and-half years saga in which the government has resisted demands to have Asif Ali Zardari investigated, arguing that as head of state he enjoys immunity.