Venezuela's top court, made up of judges loyal to President Nicolas Maduro, said the National Assembly's decision to rejoin the Inter-American Treaty of Reciprocal Assistance (TIAR) on Tuesday had no legal basis.

Maduro's predecessor and mentor, late president Hugo Chavez, withdrew the country from the defense pact, which involves 17 countries including the United States, seven years ago.

Opposition leader Juan Guaido said on Tuesday that re-joining the treaty would let Venezuela establish "international alliances" to "protect and defend the people and Venezuelan sovereignty."

The Supreme Court has annulled every decision taken by the National Assembly -- the only government institution in opposition hands -- since declaring it in "contempt" in 2016.

Venezuela was thrust into a political crisis in January when Guaido declared himself acting president, in a direct challenge to Maduro's authority. He is demanding Maduro step down so that new elections can be held.

The opposition has branded the socialist leader a "usurper" over his re-election last year in a poll widely viewed as rigged.

Guaido has since been backed by more than 50 countries, including many of those in the TIAR.

The TIAR was originally ratified by 23 countries at the start of the Cold War, but five of those -- at the time all under leftist governments -- left in 2012 while Mexico distanced itself in 2004.

Bolivia, Ecuador, Nicaragua and Venezuela left over Washington's refusal to take Argentina's side in 1982 after it invaded the British-ruled Falkland Islands. It said US inaction meant the defense pact was meaningless.