"Lebanon has become the third country in the region to see its population of registered Syrian refugees and people waiting for registration (exceed) the 100 000 mark," the UNHCR said in a statement.

As of Monday, the official number of Syrian refugees in Lebanon stood at 101 283.

Turkey and Jordan have already seen the number of Syrian refugees in their countries pass the 100 000 mark, and according to the UNHCR, there are now more than 358,000 Syrians registered as refugees in neighbouring countries.

In the case of Lebanon, none of the fleeing Syrians in the country live in camps but are all instead living within local communities, Melissa Fleming, the UN agency's chief spokeswoman told reporters in Geneva.

Many of them, she stressed, have yet to register as refugees, meaning the actual numbers are likely far higher.

Governments in the region, as well as the UN refugee agency, believe "that many more will cross borders, but at the same time, many of those who are already in the country are going to come forward and as their resources dwindle," she said.

The unrest in Lebanon in recent days has not reduced the number of Syrians flooding into the country, Fleming said, adding though that it had affected the UNHCR refugee registration operations, including in Tripoli in the north, Aka, Beirut and Saida in the south.

"We are assessing the security situation and hope to resume all operations as soon as conditions allow," the UNHCR said.

Lebanese troops deployed in Sunni areas of the capital as more sectarian violence erupted, stoking fresh fears after a top security official was killed in a bombing blamed on neighbouring Syria.

Turkey had meanwhile registered 101 834 Syrian refugees living in camps as of October 17, while another 70 000 people were living outside the camps.

The agency stressed the urgent need for funds, pointing out that nearly four weeks after it appealed for $487.9 million, it had received only a third of the money it needs to help up to 710 000 Syrian refugees in neighbouring countries by the end of the year.