Kerry said the USD 400 billion deal was "not a sudden response" to events in Ukraine, adding that the ex-Soviet state was in a "constructive moment" that could allow Ukrainians to determine their futures.
"I don't personally think that Russia signing a deal with China for gas that they have been working on for 10 years has any impact on what is about to happen in Ukraine," Kerry said during a visit to Mexico.
The agreement represents a turn to the east by Moscow at a moment when its geopolitical assertiveness, particularly the takeover of Crimea, has seen it heavily criticised by the West.
Kerry, meanwhile, welcomed Russian President Vladimir Putin's decision to withdraw troops stationed along the border with Ukraine.
"If that happens, and we are watching carefully, that's extremely constructive, it's positive," Kerry said.
"We in fact are in a good moment, not a moment of one party outwinning another, but at a constructive moment where there is the possibility of the people of Ukraine being able to determine their future, and all of us trying to find a way to further de-escalate this crisis.