Major global wheat exporters Ukraine and Russia see positive signs in discussions which could lead to the resumption of Ukrainian Black Sea grain exports after Wednesday's talks in Istanbul, their officials said. Russia, Ukraine, Turkey and the United Nations are due to sign a deal next week aimed at resuming Ukraine's grain exports, Turkish defence minister Hulusi Akar said after the talks, although U.N. chief Antonio Guterres was a little more cautious. Ukraine is "definitely a step closer to a result", the country's infrastructure minister Oleksandr Kubrakov told Reuters on Thursday.