"The Myanmar ambassador was also reminded of our call for an immediate end to the violence perpetrated by the Myanmar military regime, the release of all those arbitrarily detained since the coup in February 2021 and the establishment of a dialogue process including all stakeholders," the source added.

The executions announced Monday are Myanmar's first in decades and have heightened fears that more will follow, prompting calls for tougher international measures against the already-isolated junta.

Among the four executed were Phyo Zeya Thaw, a former lawmaker from Aung San Suu Kyi's National League for Democracy (NLD) and veteran democracy activist Kyaw Min Yu -- better known as "Ko Jimmy".

Both were sentenced to death under anti-terrorism laws.

Myanmar's junta has hit back at international condemnation of its use of capital punishment, saying the four executed prisoners "deserved many death sentences".