Swiss federal prosecutors have set up a task force to pursue potential sanctions-busting and gather evidence of war crimes connected to Russia's invasion of Ukraine.

Pressure has increased on Switzerland - a popular destination for Moscow's elite and a holding place for Russian wealth - to more quickly identify and freeze assets of hundreds of sanctioned Russians.

The Office of the Attorney General (OAG) said on Tuesday it had established a task force to examine potential sanctions violations generally outside its remit and to help pursue other potential crimes.

"At present, the focus is primarily on the areas of international criminal law and the Embargo Act," it said in a statement, referring to Switzerland's sanctions law.

Ukrainian President Volodymyr Zelenskiy on Saturday urged Switzerland to crack down on Russian oligarchs he said were helping wage war.

The State Secretariat for Economic Affairs (SECO), the agency in charge, has been swamped with asset reports and faced criticism for being underprepared and understaffed.

"Switzerland is doing more than one might have thought, but it is still doing too little," Fabian Molina, a member of parliament for the Social Democrats, told Reuters. "SECO has always been very cautious about sanctions. The department is also very small and was poorly prepared."

Pursuing sanctions violations and ordering seizures does not usually fall under the OAG's remit, but it said it was able to investigate violations if SECO requested it.

"The OAG stands ready to act quickly and efficiently if provided the jurisdiction," it said.

The task force is also looking to help gather evidence as the International Criminal Court investigates possible war crimes in Ukraine. It could open its own proceedings should any suspects enter Switzerland.

The OAG said it had suspended requests for legal cooperation from and to Russia, and was considering extending its efforts to look at economic crimes and other violations committed in relation to the war.