Tribal clashes have left at least 16 people dead and more than a dozen injured in an area northwest of the Yemeni capital, local officials and tribal sources said on Saturday. Violence, sparked by land disputes, erupted last week in four separate incidents in the Monabeh area of Sa'dah province, about 260 kilometers (160 miles) northwest of San'a, the officials said.Tribal fighting is common in Yemen, an impoverished country at the southern tip of the Arabian peninsula that has long been awash in small arms. Kalashnikov rifles and rocket-propelled grenades were used in the latest fighting, the sources said. Nine people were killed and eight injured in clashes between the Botain and the al-Ayash tribes. On-and-off fighting between the two tribes abated last March after reconciliation efforts from authorities, but erupted against last week. It wasn't clear why. In a separate feud, four people from the al-Kathir and al-Mohammed tribes were killed and six injured. Three other people were killed in two further incidents. Officials said some of the clashes were continuing.