A large explosion hit cars accompanying United Nations ceasefire monitors in the southern Syrian province of Deraa on Wednesday, according to activists and state TV.

Up to eight Syrian guards were reportedly injured in the blast.

There have been no reports that any U.N. personnel were injured, but a local television channel said a number of cars were damaged, including one belonging to Syrian state media.

One Syrian soldier described what happened.

(SOUNDBITE) (Arabic) UNIDENTIFIED SYRIAN SOLDIER, SAYING:

"We were accompanying the delegation and after we crossed the checkpoint in 100 metres, the bomb exploded. A subaltern and five soldiers were injured. I am one of them. This means six soldiers and a subaltern."

Seventy unarmed observers are now in Syria -- travelling between cities and towns where violence has flared.

The number of truce monitors is expected to double this week, and increase to 300 by the end of the month.

Travis Brecher, Reuters