JERUSALEM (AFP) - Israeli security forces went on high alert on Wednesday, mounting road blocks and additional patrols for fear that militants had infiltrated into central Israel, officials said.

"A security alert has been declared and we have stepped up patrols," said police spokesman Micky Rosenfeld, declining to give details of the threat.

Israeli rescue services said they were putting extra ambulances on standby.

Public radio said there were warnings that Palestinian militants could have infiltrated into Israel near the central city of Kfar Saba.

Television pictures showed police searching cars on major roads, causing long traffic jams.