Later in a White House briefing, Press Secretary Sarah Sanders appeared to walk back the president's words, saying that military options still were being discussed.
An adviser to Syrian President Bashar al-Assad likened President Donald Trump's threats of a missile strike to the "delirium" of a losing sports team, saying her country and its allies are ready for a USA -led war if it happens.
Speaking on TF1 television, Macron said "we have proof that chemical weapons were used, at least chlorine" in recent days by Syrian President Bashar Assad's government.
Before that, Abe will meet Trump in the United States next week with the aim of getting Japan's interests on the agenda of a proposed meeting in May or June between Trump and North Korean leader Kim Jong Un.
The U.S. and its allies have threatened to take military action in response to an alleged chemical attack last weekend.
He said even if the investigative team verifies the use of chemical weapons, "we will not know who did it".
Moscow on Thursday called on the West to "seriously consider" the consequences of threats against Syria after the United States and France said they would respond to an alleged chemical attack.
"Nevertheless we hope that common sense will prevail in the end", he said, in a meeting with new Russian ambassadors.
Prime Minister Theresa May held an emergency cabinet meeting to discuss joining mooted strikes by the U.S. and allies, with ministers agreeing "on the need to take action", her Downing Street office said in a statement.
A United Kingdom -based Syrian monitor says that troops have been emptying airports and bases, while opposition fighters have told Sky News Arabia that government-allied forces have been retreating from some positions and moving equipment.
He has said that any French strikes would target the Syrian government's chemical facilities and has spoken at length with Trump since Sunday, after the first reports of a possible chemical attack in Syria emerged. Israel has said it won't let Iran entrench militarily in Syria, and Prime Minister Benjamin Netanyahu took the occasion of Israel's Holocaust Remembrance Day to warn Tehran not to test his country.
Formally, the prime minister has the right to go to war without approval from parliament, but a convention has been established in previous conflicts where MPs have a vote either before or shortly after military action begins.
Britain continues to support the US-led coalition targeting IS jihadists in Iraq and Syria, and has conducted more than 1,700 strikes. Moscow, Tehran and Damascus have all denied responsibility for the attack.
With Russian military assistance, al-Assad launched a military offensive on Eastern Ghouta, which had been under rebel control since mid-2013.