Lebanon plans tighter entry requirements for Syrians, a senior Lebanese security official said on Saturday, as it tries to stem the flow of refugees from its larger neighbor.Lebanon hosts more than a million Syrian refugees and has the highest per capita concentration of refugees in the world. It already started last year to limit the entry of people fleeing the Syrian civil war.From Monday, Lebanese authorities will require that Syrians at the border provide the purpose and length of their stay, said Major General Abbas Ibrahim, the head of Lebanon's General Security apparatus.Syrians do not require visas for Lebanon, and Ibrahim said this was still the case. However, the paperwork required of Syrians for entry into Lebanon, as published in a list on the General Security office website, is similar to that needed by other foreigners for a visa.The announcement appeared to formalise existing restrictions. The United Nations refugee agency UNHCR says the number of Syrians registering in Lebanon on a monthly basis has dropped by half since mid-2014."We understand the reasons why governments are introducing these policies," said UNHCR spokesman Ron Edmond, referring to Lebanon and Jordan, which he said had also restricted refugees from entering."They have borne a huge burden in accepting so many refugees, but at the same time we want to ensure that people are not pushed back into situations of danger."There was concern the new rules did not mention what would happen in the case of especially vulnerable people, he said.Lebanon said in October it would admit people who needed immediate international protection on a case-by-case basis, he said. It was not immediately clear whether this policy would continue under the new rules.