BEIRUT (Reuters) - Saudi Arabia said on Friday a Saudi citizen had been kidnapped in Lebanon, a country with which it is in a diplomatic crisis. Saudi Arabia, Kuwait, the United Arab Emirates and Bahrain have advised their citizens against traveling to Lebanon and urged those already there to leave, as tensions rise in what is seen as a new front line in the regional rivalry between Saudi Arabia and Iran. Top Lebanese government officials have said they believe Saudi Arabia is holding Saad al-Hariri who resigned as Lebanese prime minister from there last weekend. Riyadh says Hariri is a free man and he decided to resign because Iran-allied Hezbollah was calling the shots in his government. The Saudi embassy in Beirut announced the kidnap of one of its citizens, but gave no details of the person s identity of the circumstances of the abduction.  The embassy is in contact with the highest ranking Lebanese security authorities about securing the unconditional release of a kidnapped Saudi citizen as soon as possible,  it said in a statement quoted by the Saudi state news agency SPA. Lebanese Interior Minister Nohad Machnouk said on the Lebanese state news agency the safety of Saudi residents and visitors was a priority for the Lebanese authorities. He added that  security services are on high alert to prevent any attempt of exploiting the current political situation from anyone and for whatever reason.   Tampering with the security and stability of Lebanon is a red line.  