German Foreign Minister Frank-Walter Steinmeier "and I agreed that continued military support for the regime by Russia or any other country risks the possibility of attracting more extremists and entrenching Assad and hinders the way for resolution," Kerry told reporters after a meeting with his German counterpart.
Washington has been concerned over reports of a Russian military build-up in Syria as a boost to President Bashar al-Assad.
Russian President Vladimir Putin's spokesman said Friday that Moscow would consider any request for troops from Assad.
Turning his attention to the issue of how to handle the tens of thousands of migrants currently fleeing Syria and elsewhere, Kerry said the United States will take in more refugees worldwide in the next two years, including 10,000 Syrian asylum seekers in 2016.
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Syrians fleeing the fighting at home make up a large proportion of the tens of thousands of desperate migrants seeking to start a new life in Europe.
In the fiscal year ending September 2015, the world's biggest economy took in 70,000 refugees.
The White House had already announced last week that President Barack Obama had asked for at least 10,000 Syrian refugees to be admitted into the US in the next fiscal year.
Kerry praised Germany's stance in welcoming a massive influx of asylum seekers as Europe grapples with its biggest migration crisis since World War II.