AL-ARISH, Egypt, Aug 12 (Reuters) - A group of armed men opened fire on Sunday on peacekeeping troops in Egypt's Sinai peninsula on the border with Israel, a security source in Sinai said.

"The attack happened in Um Shyhan area in the middle of Sinai but no one got injured," the source said.

The incident came just days after the start of a military operation in the area against militants suspected of being behind a bloody attack on Egyptian boarder guards last Sunday, which killed 16.

A group of armed men had earlier clashed with Egyptian security forces near the scene of the latest attack after they opened fire at a police checkpoint, the same security source said. No one was injured.

Police checkpoints have come under a series of similar attacks by armed assailants since last Wednesday.

Egypt sent hundreds of troops and armoured vehicles into North Sinai on Thursday to tackle militants operating near the border in an offensive that commanders said had killed up to 20 people they deemed terrorists.

The Egyptian army captured six people it considered "terrorists" in Sinai on Friday and the security source said three of them were later released.