Rwanda has accused government forces in the Democratic Republic of Congo of deliberately shelling its territory, killing a woman and wounding her baby.
Ten bombs fell on Rwandan territory on Thursday and the “provocation can no longer be tolerated”, said Foreign Minister Louise Mushikiwabo.
A Congolese army spokesman denied the allegations.
UN and Congolese forces have been pounding M23 rebels on the Congolese side of the border since last week.
DR Congo and the UN accuse Rwanda of backing the M23, a charge it denies.
BBC Great Lakes service editor Ally Yusuf Mugenzi says that even when Rwanda twice invaded Congolese territory during the 1990s, it never made such strong accusations against the Congolese army.