The delegations include foreign ministers from the three countries and other senior officials. They are being held at a venue on the grounds of Dolmabahce Palace on Istanbul's Bosphorus Strait. <br><br> The talks come shortly after the U.S., Ukrainian and Turkish delegations met at the same place in an effort to reach an agreement to eventually end the war between Russia and Ukraine. <br><br> A Ukrainian diplomatic source earlier told Reuters that Russia is demanding that talks with Ukraine in Istanbul take place without U.S. and Turkish representatives, adding the move showed Moscow was "undermining the peace effort." <br><br> "Yet another sign of the Russian side undermining the peace effort. We came to have a serious conversation, while (the) Russians are putting forward demands, conditions. This makes us doubt whether (Russian President Vladimir) Putin sent them to solve issues or just stall the process," the source said on condition of anonymity. <br><br> "There is only one reason for the Russians to be afraid of having the U.S. in the room - they came to stall the process, not solve issues, and they want to hide this from the United States." <br><br> The Ukrainian delegation is headed by Defense Minister Rustem Umerov, while Vladimir Putin's advisor Vladimir Medinsky leads the Russian team, Polish Press Agency PAP reported.