Four people were killed and three injured in clashed that erupted in Yemen between security forces and tribal militants in the province of Ma’rib, east of Yemen.Local sources in the province said tribal militants blocked the highway between Ma’rib and the capital Sana’a to demand the employment of a number of their sons in oil companies.The source added that security forces clashed with the militants while attempting to open the highway to traffic, explaining that four militants were killed and three soldiers were wounded during the clashes.