Rwanda's foreign minister has indicated in social media that Rwandan troops could enter Congo.

Louise Mushikiwabo said on Twitter late Thursday that Rwandan troops are not currently in Congo, and added the word "yet" in parentheses.

She also wrote: "When they are, you will know" in a Twitter message directed to the TV news outlet Al Jazeera.

Fighting from the war in eastern Congo that pits U.N. and Congolese forces against M23 rebels spilled over into Rwanda Thursday when multiple shells landed inside the country. In New York, the U.N. said the firing originated from positions held by M23.

M23's ranks are swollen with undercover Rwandan soldiers, according to repeated reports by the United Nations Group of Experts. Rwanda denies it supports M23.

Mushikiwabo had said earlier the shells were fired by Congo troops. She later said Rwanda doesn't care who fired the shells but only that the shelling ends.

Mushikiwabo said a projectile fired by Congolese forces at 9:45 a.m. Thursday killed a woman and seriously injured her 2-month old baby in a market in Rubavu town, located 3 kilometers (2 miles) from the Congolese border. She said Rwanda has remained restrained "for as long as we can" but that provocations can no longer be tolerated. "We will not hesitate to defend our territory," she said.

In New York, the United Nations said the U.N. force "can confirm firing incidents into Rwandan territory originated from M23 positions" from Aug. 22-29, and stressed that "it has not witnessed any Congolese Armed Forces firing into Rwandan territory during this period."

Goma, a Congolese city of 1 million located on the Rwandan border, briefly fell to the M23 rebels last year. The soldiers from Rwanda join the M23 in small groups, hiking across footpaths into Congo, the United Nations Group of Experts has said in a report. Rwanda has also supplied them with arms and sophisticated equipment, including night vision goggles, the report said.

The fighting in recent days has been among the most intense in the past year, and comes after the United Nations Security Council in March authorized the creation of a special intervention brigade which, unlike the other 17,000 peacekeepers stationed in this vast nation, has a mandate to go on the offensive against the M23. The brigade, made up of soldiers from Tanzania and South Africa, was created in the wake of the criticism following the fall of Goma to the rebels last year.