People in Lebanon have been voting in two by-elections that could heighten internal tensions in the already divided country. Voters are choosing successors to two anti-Syrian politicians whose supporters say were killed by pro-Damascus agents.The more contentious ballot, in north Beirut, pits two Christian candidates with opposing views on Syria. Former President Amin Gemaye,is the father of Pierre Gemayel who was killed in an attack last November, is a key player in the ruling anti-Syrian coalition. He is facing a tough challenge from a candidate supported by Christian leader Michel Aoun. The other vote, in a Sunni Muslim district of Beirut is a much less bitter contest A candidate from the main Sunni group of Saad-al Hariri looks set to win. But the validity of the elections themselves has been challenged by the pro-Syrian opposition. They were called without the required approval of President Emile Lahoud, a supporter of Damascus.