Rwanda's president has accused Burundi's leaders of killing their own people as human rights activists accuse security forces of killing 11 people over the weekend.
Paul Kagame's comments could cause tensions between the neighbouring countries to rise.
He made them after Burundi's president, Pierre Nkurunziza, repeatedly accused Rwanda of precipitating violence and instability in Burundi.
"Are these leaders or what, who kill their own people from morning to evening, dump them on the street and in streams, and then stand up and start accusing Rwanda?" Kagame said in a speech that was released on Sunday.
Activists said that about 200 people have been killed in Burundi since April, when Nkurunziza announced his intention to seek a third term, which his critics said was unconstitutional.
Nkurunziza, however, went on to win an election that was boycotted by the opposition in July.
The latest violence occurred on Saturday night in Bujumbura when nine people were executed
at a bar, human rights groups said.
It was not clear who the assailants were, witnesses said, but the killings occurred as a deadline given by Nkurunziza for "criminals" to surrender illegal firearms or be treated as enemies of state approached.
The slayings came a day after police killed the son of a prominent human rights activist in Bujumbura. Willy Nzitonda, whose father was a critic of Nkurunziza, was killed in the Mutakura area.
Willy Nzitonda, who had been working for the Association for the Protection of Human Rights and Detained Persons, had been arrested Friday morning before he was killed.
His father, Pierre-Claver Mbonimpa, was shot and wounded by unknown assailants in August. Mbonimpa's son-in-law, Pascal Nshirimana, was killed in Bujumbura by unknown attackers in September.
Kagame charged that Burundi is in intensive care and said its leaders are to blame because they started their country's problems.
Both Rwanda and Burundi have similar ethnic make-ups.
They are dominated by the Hutu and Tutsi ethnic groups. About 800,000 Tutsis and moderate Hutus were killed in Rwanda's 1994 genocide.
A 1993-2006 civil war in Burundi was touched off by a similar ethnic conflict. It killed 300,000 people.
The International Crisis Group has warned that the country risks sliding back into conflict.
More than 210,000 people have fled the country since April. Zeid Raad Al Hussein, the UN human rights chief, is set to brief the UN Security Council on the situation in Burundi on Monday.