MUMBAI: BJP's key ally in the NDA, the Shiv Sena castigated External Affairs Minister Salman Khurshid here today for his remarks against Narendra Modi and said he should prove himself first."If he (Khurshid) calls Modi impotent, then he should prove himself," Shiv Sena chief Uddhav Thackeray told reporters on the sidelines of an event here today.The External Affairs Minister had stoked a controversy by calling Modi "impotent" and insisted that he did nothing wrong as there was no other appropriate word to describe him in the context of the 2002 Gujarat riots.Thackeray leader also slammed Union Defence Minister A K Antony for the fire onboard submarine INS Sindhuratna, which killed two officers, saying that the naval chief's resignation would not stop such mishaps."The government must tell us how these incidents will stop occurring. Facts should come to the fore. The presence of the defence minister is not felt. Resignation alone will not stop these mishaps," he said.