In a statement, White House press secretary Sean Spicer said that the United States had detected evidence of preparations for a chemical attack, similar to the preparations that occurred before an attack in April.
Russian lawmakers on Tuesday dismissed the USA warning of a possible chemical attack by the regime of Syria's President Bashar al-Assad as a "provocation" aimed at justifying its own plan to strike the Syrian government forces.
"We want to clarify that all relevant agencies. were involved in the process from the beginning", White House spokeswoman Sarah Sanders said, noting that the State Department, Pentagon, CIA and Office of the Director of National Intelligence were involved.
"If Mr. Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price", he added.
Assad's visit to Hmeimim is his first declared tour to the base which has been run by the Russian forces since 2015 when they intervened to aid the Syrian government forces in the face of the foreign-backed insurgency, Xinhua news agency reported.
The White House did not respond to requests for details about a possible United States response, nor the intelligence that prompted the statement.
A non-governmental source with close ties to the White House said the administration had received intelligence that the Syrians were mixing precursor chemicals for a possible sarin gas attack in either the east of south of the country, where government troops and their proxies have faced recent setbacks.
The Navy launched Tomahawk missiles at a Syrian military airfield April 6 in response to a previous alleged chemical weapons attack, using two guided-missile destroyers in the eastern Mediterranean Sea, the USS Ross and USS Porter, to do so.
Russian Federation and Iran are both staunch backers of the Assad regime.
Jeff Davis, a Pentagon spokesman, said Tuesday the activity at the Shayrat air base indicates "active preparations for chemical weapons use".
The U.S. attack on a Syrian air base came after years of heated debate and deliberation in Washington over intervention in the bloody civil war.
The two groups said the US -led coalition was behind the strike.
But the visit to the Hmeimim base comes at a time when the USA warned there are "potential preparations for another chemical weapons attack" by the Syrian government forces and warned Assad that he would face a "heavy price" if it is carried out.
"Any further attacks done to the people of Syria will be blamed on Assad, but also on Russia & Iran who support him killing his own people", Haley wrote.
Syria denied using chemical weapons.
The White House statement on Monday night was made without forewarning and caught State Department officials by surprise.