A US think tank believes Russian President Vladimir Putin is so confident that his country will be victorious in Ukraine that he is not considering a ceasefire.

Putin told Russian media outlets on Thursday that Russia cannot allow Ukraine to take advantage of a ceasefire to improve its positions.

Putin spoke to reporters again on Friday. He said a condition for a ceasefire would be the withdrawal of Kyiv's forces from the four Ukrainian regions that Russia has unilaterally annexed.

The Institute for the Study of War released an assessment on Friday. It said, "Putin's rejection of any ceasefire indicates that he is increasingly confident in his assessment that Russia can pursue victory by continuing creeping advances in Ukraine, outlasting Western support for Ukraine, and winning a war of attrition against Ukrainian forces."

The think tank stressed that the West must quickly provide Ukraine with the support it needs to conduct counteroffensive operations, so that a peace deal acceptable to Ukraine and its partners can be secured.

Ukrainian forces remain determined to hold their lines and positions. They also want to retake some of the territories that Russia is occupying.

Kyiv has been calling for Western military assistance ahead of a summit that will be attended by representatives of NATO member states. The meeting is scheduled to begin in the US on July 9.