Algeria has barred all Syrians from entering the country through its southern border to prevent infiltration by Syrian opposition groups into their territory as a security threat, a senior official said.

Director of immigration policy at the Interior Ministry, Hassan Qasimi, told Reuters the Syrians, seeking asylum in Algeria in this way, were suspected of being Islamist militants and were not welcome.

"We have hosted 50,000 Syrians in the past few years for humanitarian reasons," he said, referring to refugees who fled the civil war. "But we cannot welcome members of armed groups fleeing Syria when it comes to our security."

He said about 100 people had arrived at the southern border with the help of local armed escorts in the past few weeks but had been spotted and expelled shortly after infiltrating into Algeria.

"These Syrians arrived via airports in Turkey, Jordan, Egypt, Sudan, Niger or Mali using fake Sudanese passports," he said.

"Absolutely this is a criminal network and we have to be very vigilant so we do not allow them to enter Algeria," he said.

Algeria having maintained diplomatic ties with Syria throughout the civil war, during which President Bashar al-Assad largely defeated the opposition militants and militants trying to topple him. Syrians do not need visas to enter Algeria.

South and southeastern Algeria are largely desert and empty, but have strengthened their security presence there after various militant and rebel groups have spread in Libya, northern Mali and Niger.