Hutu rebels killed women and children at a refugee camp

The meeting in Tanzania was attended by Thabo Mbeki of South Africa - which has been mediating in the conflict - and five other heads of state.

Burundi is struggling to emerge from a civil war between rebels from the Hutu majority and the Tutsi-dominated army.

Most former rebels have joined the government - but a radical Hutu group has continued to fight.

The group, the FNL, claimed responsibility for last week's killing of about 160 Congolese Tutsi refugees in Burundi.

'Terrorism'

Burundi's leading Tutsi and Hutu parties signed a power-sharing agreement earlier this month.

It is intended to form the basis for a new constitution and to pave the way for elections.

Survivor tells of massacre Q&A: Burundi massacre

Under the deal, the Tutsi minority will have 40% of government and national assembly posts, compared to 60% for Hutus.

However some Tutsi politicians say they are excluded, and want greater constitutional guarantees ahead of the elections scheduled for October.

But the BBC regional analyst Robert Walker says the FNL poses a bigger challenge to the peace process.

The leaders meeting in Dar es Salam summit declared the group a "terrorist organisation".

Mr Mbeki and his Tanzanian, Mozambican and Zambian counterparts urged the African Union and UN Security Council to do likewise.

The FNL has consistently refused to join Burundi's peace process, and claimed last Friday's massacre of Congolese Tutsi refugees in Western Burundi.