Yemeni military officials say a suicide bomber has killed four tribal militiamen allied to the army who were advancing on an al-Qaeda-held town in the country's south, AP reported.

They say the attack happened in the town of Umsurra on Monday, June 4 as they were moving to reinforce a new army offensive against the nearby coastal town of Shaqra.

Officials also say Yemeni warplanes continued strikes against al-Qaeda positions in Zinjibar, the capital of Abyan province, and the militant stronghold of Jaar. Both have been held for over a year by militants who took advantage of Yemen's political turmoil to seize broad swaths of the south.

They spoke on condition of anonymity in line with regulations.