President-elect Donald Trump. REUTERS/Mike Segar European leaders wrote a letter to President-elect Donald Trump on Monday warning him that "the prospect of a new grand bargain with Russia" would endanger the "predictability and security" Americans and Europeans achieved together after the end of the Cold War.

The letter, signed by 17 current and former officials from a range of central and eastern European countries — including Bulgaria, Romania, Estonia, Latvia, and Sweden — argued that it would be "a grave mistake" to roll back the current sanctions on Russia or accept its aggression in Ukraine.

"The aftershocks of such a deal would shake American credibility with allies in Europe and elsewhere," the letter said. It also said "the rules-based international order on which Western security has depended for decades" would be eroded by an acceptance of Russian President Vladimir Putin's disregard for international law.

"Have no doubt: Vladimir Putin is not America's ally," the letter said. "Both of the presidents who preceded you tried in their own ways to deal with Russia's leadership in the spirit of trust and friendship. Big mistake: Putin treated their good intentions as opportunities."

President Barack Obama pursued a "reset" of the US relationship with Russia shortly after taking office in 2009 that ultimately failed. As The Washington Post's Josh Rogin reported, central and eastern European leaders wrote a similar open letter to Obama at the time of the reset "to ensure that too narrow an understanding of Western interests does not lead to the wrong concessions to Russia."

Russian President Vladimir Putin. Kirill Kudryavtsev/Reuters

Russia's annexation of Crimea, incursion into eastern Ukraine, and support for far-right and white supremacist movements across Europe — as well as the Russian hacking campaign targeting US Democrats during the presidential election — has fomented a greater urgency in the European warnings to approach the Kremlin with caution.

"Putin does not seek American greatness. As your allies, we do," the letter said. "A deal with Putin will not bring peace. On the contrary, it makes war more likely. Putin views concessions as a sign of weakness. He will be inclined to test American credibility in frontline NATO allies, such as Estonia, Latvia, Lithuania, and Poland."

Throughout the presidential campaign, Trump questioned the value of NATO, which is currently engaging in the biggest military buildup on Russia's western borders since the Cold War.

"As your treaty-bound allies," the letter concluded, "we appeal to Americans in the new US administration and Congress to stand firm in the defense of our common goals and interests: peace, Atlantic strength, and freedom. United, we are more than a match for Russia's ailing kleptocracy. Divided, as we have seen all too clearly in recent years, we are all at risk."