The United States has warned the Venezuelan authorities of a "swift and strong response" to any threat to opposition leader Juan Guido, who has returned to the country.

"Guido's safe return to Venezuela is of the utmost importance to the United States," Vice President Mike Bens wrote on Twitter as Guido arrived in Caracas on Monday.

He added that he would not tolerate threats or acts of violence or intimidation against him, and will respond quickly, as he put it.

Guido, who heads the National Assembly, has declared himself acting president and has been recognized by some 50 countries, including the United States, and is threatened with arrest for failing to comply with a decision to stop him from leaving Venezuelan territory.

In turn, US National Security Adviser John Bolton said in a tweet via Twitter that any threats or action against Guido would be met with a strong and significant response from the United States and the international community.

These statements coincided with the arrival of Guido to his country, where he was received by a crowd of supporters with a number of ambassadors of European and Latin American countries.

"We are here to witness democracy and freedom, and to enable President Guido to return," said French Ambassador to Caracas Roman Nadal.

For his part, German Ambassador Daniel Kreiner said he attended the airport "to ensure the return of the President of the National Assembly without hindrance to his country."

"We will continue to move in the street and mobilize continuously; we are here in Venezuela," Guido told his supporters.

On Sunday, Guido announced his intention to return from Ecuador to the country and participate in demonstrations planned by the opposition organized throughout the country.

On February 23, Guido headed for Colombia, before heading to Brazil, Paraguay, Argentina and Ecuador, as part of Venezuelan opposition efforts to bring in humanitarian aid to the country sent by the United States, but the Venezuelan army blocked the aid and closed the border with Colombia. Maduro is part of the US strategy to occupy Venezuela.