"The U.S. government has limited ability to provide emergency services to U.S. citizens" in the country, the advisory warned.
China said, "History has taught us that external interference or sanctions, instead of helping solve problems, can only complicate matters."
"In the face of any aggression, of any nature and intensity, we will defend Venezuela, as it belongs to us," said Defense Minister Vladimir Padrino, who is standing by embattled President Nicolás Maduro.
White House national security adviser warned of a "significant response" to any harm that came to U.S. citizens at the hands of Venezuela.
The State Department is not saying when it will implement the sanctions, noting that there is no deadline in the law for imposing them.
"The Treasury Department seems to be doing its damnedest to help a Russian oligarch by relieving sanctions, hiding the evidence and duping the Senate in the process," John Avlon said.
"It definitely rattled people," a former senior U.S. administration official told The Wall Street Journal. "People were shocked. It was mind-boggling how cavalier they were about hitting Iran."
"The Americans happily say that these sanctions are unprecedented in history. Yes, they're unprecedented. And the defeat that the Americans will face will be unprecedented, God willing," Supreme Leader Ayatollah Ali Khamenei said.
Trump's style of dealmaking is leading to some questionable policy decisions.
North Korean Organization and Guidance Department Director Choe Ryong Hae, often described as Kim Jong Un's second-in-command, was included in the new U.S. sanctions.
Although the context of Meng Wanzhou's arrest is alleged violation of the sanction on Iran, U.S. unease with the Chinese company runs much deeper—and a constructive resolution of the trade war has just become a lot less likely.
In response to mounting pressure to punish ally Saudi Arabia, President Donald Trump has instead accused the "terrorist nation" of Iran for unrelated acts.
"The United States is a regime formed on the basis of capitalism, racial discrimination and hegemonism," Major General Mohammad Ali Jafari said.
Nathan A. Sales, the State Department's ambassador-at-large and coordinator for counterterrorism, called Iran "an extraordinary compendium of evil."
Oil prices have dropped significantly, with the U.S. benchmark price dipping below $60 per barrel.
At least 16 bases were continuing research.
Economy Minister Bruno Le Maire also stressed that tensions with the U.S. over Iran revealed the need for the EU to "affirm our independence."
"We will not obey such sanctions," Turkish President Recep Tayyip Erdogan said, adding that his government saw Washington's move as "violating the global balance."
The crown prince has threatened to develop nuclear weapons if Iran is able to do the same.
"U.S. bullying is backfiring," Foreign Minister Javad Zarif warned earlier on Monday.
The "people's food basket has shrunk, except for the profiteers of sanctions," said one civil servant living in Tehran.