KIEV - Ukraine on Friday charged a prisoner swap negotiator with plotting to assassinate President Petro Poroshenko and other senior officials by attacking their homes and offices with mortar fire and grenades.

Volodymyr Ruban was detained on Thursday with a haul of firearms and ammunition in his vehicle while crossing the “grey zone” splitting Russian-backed eastern insurgents from the rest of Ukraine.

The 50-year-old Ukrainian national is known to have organised several prisoner exchanges between the two sides during four years of fighting, in which more than 10,000 have died.

“Ruban is suspected of preparing armed attacks against senior government officials,” the presiding judge in Kiev was quoted as saying by Interfax-Ukraine news agency.

The charge sheet accused Ruban of planning to use “mortar guns, grenade launchers, light weapons and explosive devices” to attack the homes of Poroshenko and other officials.

These included Interior Minister Arsen Avakov and National Security and Defence Council chief Oleksandr Turchynov, along with former premier Arseniy Yatsenyuk and other undisclosed officials.

The judge said Ruban’s aim was to “create chaos... and help Russia launch a full-scale offensive” that would put the separatist region under its permanent control. Ruban has been in pre-trial detention for two months.

Ukrainian media had previously accused Ruban of harbouring pro-Russian sentiment and being supportive of the insurgents.

He has used his ties with the rebel commanders to orchestrate prisoner swaps dating back to the early months of the war in 2014.

Ruban told the court he did not know that the vehicle he was detained in was carrying weapons, and accused the authorities of framing him.

Poroshenko asked Ukrainian Security Service chief Vasyl Grytsak to take personal charge of the investion. “I ask you - I order you - to take this under your personal control,” Poroshenko told Grytsak in a televised meeting.

Russia rejects either plotting or backing the fighting in order to destabilise its western former Soviet neighbour as it slowly charts closer ties with the West.