But halting progress, ever-more deadly drone attacks and unmoving negotiating positions seem to have taken their toll. On Thursday, Trump used a striking analogy to concede the warfare was nowhere near over, and that he did not, at that moment, feel it was best to intervene.

Russia will respond to Ukraine's latest attacks as and when its military sees fit, the Kremlin said on Thursday, accusing Kyiv of state terrorism as U.S. President Donald Trump downplayed prospects for an immediate peace between the countries.