BEIRUT, March 25 (Reuters) - Insurgent groups fighting the Syrian government have seized control of a southern town near the border with Jordan after four days of battles, the Syrian Observatory for Human rights reported on Wednesday. A Syrian military source said there had been heavy fighting with armed groups in the town of Bosra al-Sham on Tuesday night. "We are investigating the facts in the field," the source said. The ancient city of Bosra is listed as a UNESCO world heritage site. (Writing by Tom Perry; Editing by Alison Williams)