Days after raids and several rounds of questioning, the Enforcement Directorate (ED) on Wednesday sealed the National Herald office, instructing that the premises cannot be opened without prior permission from the probe agency.

The ED had earlier carried out raids at 12 locations in the national capital and at other places in connection with the National Herald case in which top Congress leaders are accused of violating norms.

"Delhi Police blocking the road to AICC Headquarters has become a norm rather than an exception! Why have they just done so is mysterious...," Congress leader Jairam Ramesh said.

The National Herald case pertains to the alleged financial irregularities under the Prevention of Money Laundering Act (PMLA) and was registered about nine months ago after a trial court took cognisance of an Income Tax department probe carried out on the basis of a private criminal complaint filed by former BJP MP Subramanian Swamy in 2013.

The petitioner had approached the court alleging that the assets of Associated Journals Limited (AJL), which published the National Herald newspaper, were fraudulently acquired and transferred to Young Indian Pvt Limited (YIL), in which Congress leaders Sonia Gandhi and her son Rahul Gandhi owned 38 per cent shares each.

Swamy alleged that the Gandhis cheated and misappropriated funds, with YIL paying only Rs 50 lakh to obtain the right to recover Rs 90.25 crore that AJL owed to Congress.

On July 27, the probe agency questioned Congress interim-president Sonia Gandhi, after which raids were conducted. It was the third round of questioning of the senior leader in the case.

Following the summons, Congress workers and leaders staged protests in various parts of the country alleging misuse of probe agencies by the government.

Meanwhile, in June, the ED questioned Rahul Gandhi for five days also.