Republican Senator John McCain will head to Ukraine's capital for the weekend ahead of fresh protests planned by opposition activists, his office said Friday. "Senator McCain is traveling to Kiev to meet with government officials, opposition leaders and civil society as they work to determine their country's future," McCain spokesman Brian Rogers said. On Sunday, Democratic Senator Chris Murphy will join McCain, the 2008 Republican nominee who lost the White House race to Barack Obama. McCain has strongly condemned the Ukrainian government over the conflict that erupted last month when President Viktor Yanukovych backed off a deal to sign an association accord with the European Union. Yanukovych's decision followed threats from former Soviet master Russia, triggering anger from pro-European Ukrainians. "It is appalling that Ukrainian authorities have chosen to use violence and oppression against peaceful demonstrators in Maidan (Independence) Square in Kiev," McCain said in a statement earlier this week. "Such despicable conduct violates the most basic universal rights -- especially the freedom to speak and associate -- that are owed to all people." Opposition protesters meanwhile expanded their encampment in Kiev's symbolic Independence Square, as their ranks quickly swelled. "Those brave men and women should know that they are not alone. Their friends across the world stand in solidarity with them," McCain said. The United States has made its solidarity with Ukraine's opposition clear. Washington went so far as to threaten sanctions on Thursday after a failed police raid on the protest barricades. In a notable diplomatic gesture, Victoria Nuland, assistant secretary of state for Europe, mingled this week with pro-European protesters in Kiev.