As the United States and its allies supply Ukraine with increasingly sophisticated weapons, Washington is in talks with Kiev about the danger of escalation if the latter strikes deep inside Russia.
According to Reuters, citing sources, the behind-the-scenes discussions, which are highly sensitive and previously unreported, do not place explicit geographic limits on the use of weapons supplied to Ukrainian forces. But the conversations are aimed at reaching a common understanding of the risk of escalation, three U.S. officials and diplomatic sources said.
"We have concerns about escalation and yet still do not want to put geographic limits or tie their hands too much with the stuff we're giving them," said one of the three U.S. officials, speaking on condition of anonymity.
President Joe Biden's administration and U.S. allies are increasingly willing to provide Ukraine with longer-range weapons, including M777 howitzers. The Pentagon's announcement last week that Denmark would supply Ukraine with Harpoon anti-ship missiles would further expand Kiev's capabilities.
U.S. officials say the Biden administration is even considering supplying Kiev with the highly mobile M142 artillery rocket system (HIMARS), which can have a range of hundreds of kilometers depending on the ammunition.
But U.S. intelligence has also warned about growing risks, particularly given a mismatch between Russian President Vladimir Putin's apparent ambitions and the performance of his military. The coming months could put the war on a "more unpredictable and potentially escalatory trajectory," Director of National Intelligence Avril Haines told a Senate hearing this month.
The United States, by design, is not directly combating Russian forces but Pentagon commanders are in constant contact with Ukrainian leaders and have provided critical intelligence that has allowed Ukraine to target Russian troops, on land and at sea, U.S. officials have said.
A second U.S. official said Washington and Kiev have a common "understanding" about the use of certain Western weapons systems. "So far, we've been on the same page about the thresholds," the official said.
Russian Foreign Minister Sergey Lavrov warned the West that supplying Ukraine with weapons capable of hitting Russian territory would be "a serious step towards unacceptable escalation."