US President Barack Obama said he is "hopeful" but "sceptical" about a new ceasefire between Ukrainian forces and Russian-backed separatists.
The American leader, speaking at the Nato summit, confirmed that the European Union was putting together the final details of a renewed sanction plan. When asked if new sanctions would be imposed against Russia he said that was the "likely scenario".
He said that the results being seen in discussions with Russia were the result of imposed sanctions on the country and the continued threat of sanctions from Western nations.
He also warned that the implementation of the truce agreed in the Belarussian capital, Minsk, still had to "be tested".
The new ceasefire, which began at 1500 GMT today, was announced by the Organisation for Security and Cooperation in Europe's (OSCE) Heidi Tagliavini, a Swiss diplomat.
The plan is to include a stop to "active offensive operations" by both the Ukrainian military and pro-Russian rebels. It will allow international ceasefire monitoring, prisoner exchanges and humanitarian corridors to those affected by the conflict.
On other topics such as Isis (now known as the Islamic State), Obama said it is "critical we have Sunni-majority states [in the Middle East] rejecting Isis and joining an international coalition."
He added that the United States is "going to achieve our goal" of destroying the terror group, promising to do whatever it takes to ensure that the threat from the militants was countered.
The West is accusing Russia of arming and training rebels in Ukraine's restive eastern regions, a claim which Moscow denies.
UN agencies estimate more than 2,600 people have been killed in the fighting between pro-Russian separatists and the Ukrainian military since April.