Ruto, national broadcast director Joshua Sang and President Uhuru Kenyatta are suspected of committing war crimes during post-election violence that left thousands of Kenyans dead in 2007.
Trials for Ruto and Sang, described as the "voice of hate," began last month at The Hague, Netherlands.
Fatou Bensouda, chief prosecutor at the International Criminal Court, said Wednesday the Kenyan government was called on to turn Walter Barasa over to the court to face criminal charges.
"There is evidence to suggest that Walter Barasa tried to bribe someone he thought was a prosecution witness in the case against Mr. Ruto," she said.
The ICC said it had evidence to suggest there was "a network of people" trying to sabotage the case against Ruto.
The African Union expressed concern over the case to the ICC. It said summoning Ruto before the court would inhibit his ability to uphold his constitutional obligations. His case was halted briefly so he could return home to deal with last month's terrorist attacks at the Westgate shopping center in Nairobi.
The ICC last month told Kenyan journalists and other members of the press "to desist from doing anything that would reveal or attempt to reveal the identity of protected witnesses" in the Ruto case.
The chief prosecutor said it suspected witness interference was ongoing.