The Vatican issued an unheeded urgent appeal to Venezuela's leaders to suspend its new Constituent Assembly which, it says, is threatening the future of the South American nation.

The strongly worded statement, issued by the Vatican's Secretariat of State, said Pope Francis is following closely the situation in Venezuela, where President Nicolas Maduro accelerated a showdown with the opposition, as he inaugurated his bitterly-opposed new assembly.

The message came as the body's 545 delegates were installed at the legislative palace in Caracas, close to the chamber where the opposition-controlled National Assembly meets.

The Vatican had joined dozens of States in rejecting the new assembly, which it said "creates a climate of tension and conflict" in the overwhelmingly Catholic country, The Guardian reported.

The United States said will not recognise the consituent assembly, the State Department had said on Aug. 3, calling it "the illegitimate product of a flawed process," Reuters reported.

Despite the Vatican's strongly-worded statement, a Catholic priest gave his blessing at the inauguration on Friday of the body which will have the power to rewrite the constitution and dissolve State institutions.

Maduro wants the new Constituent Assembly to rewrite the country's constitution and holds powers that override all other government branches.

Opposition leaders have denounced the erosion of democracy and pledged they will only be removed by force.

More than 125 people have already been killed in over three months of violent anti-government protests.

The statement expresses "profound concern for the radicalisation and worsening of the crisis," including the increase in deaths, injuries and arrests of protesters.

It called on all of Venezuela's politicians, in particular, the government, to guarantee "full respect for human rights and basic freedoms, as well as for the existing Constitution."

The Vatican said the new Constituent Assembly should be "avoided or suspended" since its "foments a climate of tension and conflict" which "mortgages the future" of the country, rather than fostering reconciliation and peace.

The statement calls for a negotiated solution, along the lines already indicated in a previous letter from the Secretary of State on December 1, 2016.

These solutions must take into account "the serious suffering of the people", due to a lack of security, as well as the shortages of food and medicine.