The European Union and United Nations called on Friday for an urgent investigation into a mass grave discovered in the Democratic Republic of the Congo’s capital Kinshasa, which local authorities say contained hundreds of dead babies and foetuses.

At least 421 bodies were buried in the grave in Maluku district in March, including about 300 stillborn babies and foetuses “abandoned in rivers, streams and even hospitals,” the government said.

The EU office in the country called for an “urgent, transparent and credible” investigation and offered to provide support “with all means at our disposal”.

The United Nations human rights office in Geneva pushed for an investigation to be completed in a “transparent, credible and independent manner”.

The UN human rights office said it had been “working closely with the authorities over the past few weeks, including by supporting the judicial investigation into those very serious allegations”.

The UN body “was also conducting our own independent human rights investigation, including by carrying out site visits and interviewing witnesses and family members of victims”.

Former colonial ruler Belgium and rights groups, including Human Rights Watch, backed up the call for an independent inquiry.

Kinshasa’s interim governor, Luzolanu Mavema, said the government had “absolutely nothing to hide”.

The governor said he wanted to dispel rumours that the common grave could hold the bodies of government opponents who were killed during protests and mass arrests in January.

The protesters had denounced moves they claimed were designed to delay presidential elections and allow President Joseph Kabila to remain in power in defiance of the constitution. Up to 42 people died during the violent protests.