A suicide bomber killed four people on Tuesday in a residential district of southern Beirut known for its support of the powerful Shi’ite Muslim military and political movement Hezbollah, security sources said.

Tensions from Syria’s conflict have increasingly infected neighboring Lebanon. Hezbollah has sent fighters and advisers to help its ally President Bashar al-Assad, a member of the Shi’ite-derived Alawite minority, against mainly Sunni rebels.

A Reuters reporter said she saw the remains of what appeared to be the suicide attacker as emergency workers transported wounded people from the blast site, less than 100 meters from where another bomb exploded this month.