At least two Hamas officials have been killed after a suspected bomb exploded in the southern suburbs of Beirut, the Lebanese capital, a Hamas source has told Al Jazeera.

The bomb was placed under a car in the suburb of Haret Hreik on Saturday, the source said. 

Lebanese officials said that the Shia Muslim Hezbollah group had sealed off the area where the incident took place, making information concerning the reason for the blast difficult to ascertain.

A photographer for the AFP news agency said that the blast occured in an alley just metres away from a community centre where Hezbollah  was organising a ceremony to commemorate the Shia rituals of Ashoura.

The official national news agency NNA said the blast was "the result of three bombs placed under a car whose owner is said to be a member of Hamas".
  
But Hezbollah's al-Manar television, quoting unnamed security officials, said the "blast took place in an office of the Hamas movement causing casualties".

Lebanon is home to 12 Palestinian refugee camps that house more than 200,000 registered refugees.

The blast came on the eve of the first anniversary of Israel's 22-day offensive on the Hamas-controlled Gaza Strip, during which about 1,400 Palestinians and 13 Israelis were killed.