The Trump administration is calling it "a critical week ahead" as talks to end the more than three-year Russia-Ukraine war push on. President Donald Trump says the U.S. is edging closer to mediating a deal and is calling both sides to "finish it off." But Russia and Ukraine remain hesitant about the proposals. Ukraine is concerned about losing territory, while Russia worries about Western powers on its border. Trump met with Ukrainian President Volodymyr Zelenskyy in a private meeting while attending the pope's funeral in Rome over the weekend. "He told me that he needs more weapons, but he's been saying that for three years. He needs more weapons. We're going to see what happens," Trump said about the meeting Sunday. "I want to see what happens with respect to Russia."Trump is also urging Ukraine to formally surrender Crimea and the eastern part of its country, which is currently being held by Russian troops. The U.S.-negotiated peace deal may make Crimea permanently part of Russia, but there are doubts that the Ukrainian government can agree without a national referendum. Trump is also pushing Ukraine to sign a deal for U.S. aid and weapons in exchange for access to rare earth minerals. In return, Ukraine says it wants NATO membership or arms and training for giving up its territory.Secretary of State Marco Rubio warned that if both sides did not agree to a deal, the U.S. could walk away. "Right now, the only one who can bring these two sides together to end this war is our president," Secretary Rubio said in an interview Sunday with NBC's "Meet the Press." "We have to make a determination about whether this is an endeavor that we want to continue to be involved in, or if it's time to sort of focus on some other issues."Russian Foreign Minister Sergey Lavrov expressed concerns that the deal may unfairly favor Ukraine and Europe. "They bluntly stated that they can support only the deal which, at the end of the day, will make Ukraine stronger and would make Ukraine a victor," Lavrov said in an interview Sunday with CBS' "Face the Nation."Trump, who says he plans to meet with President Vladimir Putin next month, has also demanded that Russia sign the U.S.-mediated peace deal."I wanted him to stop shooting, sit down, and sign a deal," Trump said.