Ukraine's prime minister told the defence ministry on Wednesday to ensure that government forces were on full battle alert despite a 12-day ceasefire with Russian-backed separatists.

"Russia will not give us peace so I am asking the defence minister for full battle readiness," said Arseny Yatseniuk in comments in keeping with the hawkish stance he has been taking over negotiations with separatist rebels in eastern Ukraine.

Enacting the peace plan of President Petro Poroshenko did not mean "relaxing the work of the defence and interior ministries", he said. "Full readiness (is required). We can't believe anyone, especially the Russians."