Domestic militants in Tanzania currently lack the capability to inflict major damage, but the risk of attacks is likely to increase in coming months.
On 5 May, an improvised hand grenade was thrown into the grounds of St Joseph's Church in Arusha's Olasiti suburb, killing 3 people and wounding 63 others.
The attack was targeted at a large celebration attended by the Vatican Nuncio, a diplomatic representative of the Holy See.
Following sectarian unrest in Mbeya, Dar es Salaam, Zanzibar and Mwanza earlier this year, armed security at Christian sites was stepped up, especially during the lead-up to Easter celebrations.
While the Tanzanian government initially arrested several Saudi and UAE nationals (since released without charge) in connection with the bombing, the attack was most likely perpetrated by a domestic group seeking to provoke further sectarian violence between Christians and Muslims.
The improvised explosive device (IED) appears to have been competently assembled with the aim of causing maximum casualties through the use of shrapnel.
Details available on the IED's construction do not, however, necessarily indicate external assistance.
Regional groups - such as Somalia's al-Shabaab or al-Qaeda in East Africa (AQEA) - have little attack capability in Tanzania and any attacks would more likely target security forces and Western interests rather than be aimed at provoking sectarian violence.
Therefore this attack was most likely staged by a domestic group, probably Jumuiya ya Taasisi za Kiislam (Community of Muslim Organisations).
This radical Islamist organisation is headed by Sheikh Issa Ponda, who has close ties to Zanzibari Islamist groups which have sought to provoke sectarian unrest and were behind the rioting in Dar es Salaam in 1998 and October 2012.
In the likely event of future attacks on Christians, violent confrontations are likely in cities with mixed populations, such as Dar es Salaam, Mwanza, Mbeya, Arusha and Zanzibar's Stone Town.
Such violence is likely to take the form of targeted killings, arson attacks and riots.
The nature of the IED used in Arusha does not alter the assessment that emerging militant groups currently lack the capability to inflict major damage on commercial or Western targets.
However, the risk of attack on Western hotels, critical infrastructure and strategic sectors such as natural gas and mining, is likely to increase over the next two years or so, especially if domestic groups secure funding and technical support from groups such as AQEA and al-Shabaab.
Robert Besseling is the Deputy Head of Africa Forecasting at Exclusive Analysis.