The prosecutor for the International Criminal Court (ICC) Karim Khan has arrived in the DR Congo, his office said Tuesday, as the country grapples with an upsurge in fighting in the east.

The Rwanda-backed M23 has in recent weeks seized two major cities in eastern Democratic Republic of Congo, giving the armed group a major foothold in the region since taking up arms again in late 2021.

"We are extremely worried about recent developments in Congo, we know the situation particularly in the east is acute," Khan told reporters on his arrival in the capital Kinshasa.

"The message has to be conveyed very clearly: any armed group, any armed forces, any allies to armed groups or armed forces don't have a blank cheque," he said.

"They must comply to international humanitarian law," Khan added.

According to UN experts, the M23 is supported by around 4,000 Rwandan soldiers.

Since its resurgence, the fighting between the group and Congolese armed forces has provoked a humanitarian crisis in a region plagued by conflict for three decades.

"This is a moment where we will see if international humanitarian law can withstand the demands that the people of the Democratic Republic of Congo insist upon, which is the equal application of the law," Khan said.

"The people of the DRC are as precious as... the people of Ukraine, the people of Israel or Palestine, girls or women of Afghanistan," he added.

Khan is set to meet DRC President Felix Tshisekedi, government ministers, the U.N. Secretary General's country representative Bintou Keita, as well as victims of the conflict and civil society members.

The first investigation that the ICC opened after it began its work in 2002 concerned the DRC.

Since then, the court has convicted three people for crimes committed in the country.

The ICC prosecutor's office also opened an investigation in 2023 into allegations of crimes committed since January 2022 in North Kivu province in the east of the vast nation.

Khan's office, which visited the country in May 2023, indicated early this month that the current situation in eastern DRC "is part of the ongoing investigation."