The top US diplomat also acknowledged in an interview with Dubai-based Al-Arabiya television that President Bashar al-Assad was not ready to make peace.
Kerry was speaking a day after telling the opening of a peace conference in Switzerland that the Syrian leader could have no role in any future transitional government after three years of war.
Expectations are low for a breakthrough at the talks, dubbed Geneva II, which bring the opposition and the regime together for the first time since an uprising began in March 2011.
But as the UN works on trying to get both sides around the negotiating table on Friday, the United States has called for agreement on local ceasefires and improved aid access to reach stricken communities.
"If there is a peace agreement there are many countries that have already offered to step up and be peacekeepers in the new Syria," Kerry told the television station.
"There is no question, but that we are all prepared to help provide protection to any of the minorities."
But he stressed to Al-Arabiya during the interview on the sidelines of the World Economic Forum in Davos that there would not be any American boots on the ground.
While he did not name any countries, he said they would be countries acceptable to Syria.
Kerry also said that Assad was "not ready at this point and time" to make peace.
"This is a man who has committed war crimes," he added.