"I regret to say that they [warring parties] have not yet provided inventory of heavy weapons, the routes along which they intend to withdraw them, or where they will be concentrated," Alexander Hug said at a briefing.
The deputy chief monitor called on the sides to provide the mission with precise data.
Under the new agreement on Ukrainian reconciliation, Kiev forces and eastern Ukrainian fighters have to completely withdraw their heavy weapons from the line of contact to create two security zones 50-140 kilometers (30-85 miles) wide.
The 13-point peace deal, reached by the leaders of Russia, Germany, France and Ukraine last week in Minsk, also envisioned a full ceasefire in southeast Ukraine as of February 15 and a all-for-all prisoner exchange.