By Lamin Jahateh

BANJUL (Reuters) - Thousands of people lined the streets of Gambia's capital Banjul on Thursday to welcome home new President Adama Barrow days after authoritarian leader Yahya Jammeh fled into exile under pressure from regional forces.

Barrow, a former real estate agent, won a Dec. 1 election but Jammeh refused to step down, forcing his opponent to be inaugurated at the Gambian Embassy in neighbouring Senegal.

Clad in a long white African tunic, Barrow smiled as he stepped out of a small plane and walked down a red carpet to greet hundreds of diplomats and officials lined up to greet him. Immediately afterwards, fighter jets from the West African ECOWAS regional force passed overhead.

"A new page in Gambian history is being turned," said Mohamed Ibn Chambas, U.N. Special Representative for West Africa and the Sahel, who helped negotiate Jammeh's exit, shortly before accompanying Barrow to Banjul.

Barrow's surprise ballot box victory and the determination of Western and African countries to uphold it is being celebrated as a moment of democratic hope for Africa.

Yet, diplomats say tiny Gambia was an easy target and that regional armies are unlikely to venture into bigger countries to oust authoritarian rulers with more powerful allies than Jammeh.

Regional leaders helped thrash out a deal last Saturday for Jammeh to fly to exile in Equatorial Guinea as thousands of ECOWAS troops closed in after 22 years of increasingly repressive rule in Gambia, marked by alleged torture and killings of opponents.

Jammeh's political demise is a relief to many people in the small, sliver-like West African country and the U.N.'s Chambas promised assistance in investigating human rights abuses.

Swiss police detained longtime former Gambian interior minister Ousman Sonko near the Swiss capital of Berne on Thursday after a complaint filed against him by non-governmental organisation Trial International.

In the weeks following Jammeh's decision to reject the election outcome in early December, Barrow was seen as vulnerable and was protected by unarmed volunteers until he relocated to Dakar.

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During his absence, he was unable to return home for his son's funeral after a dog attack.

He has asked the 7,000-strong West African military contingent to remain in Gambia for another six months, Chambas said on Thursday. An ECOWAS official said they were studying the proposal.

Gambia, a tiny riverine nation surrounded by Western ally Senegal on three sides, has a bloated army for its size but so far there have been no signs of resistance to ECOWAS forces.

However, lingering questions remain as to the loyalty of the Republican Guard, thought to number about 400, who in the past protected Jammeh from coup attempts.

The whereabouts of members of alleged assassination squads known in Gambia as the "Junglers" were not known.

(Additional reporting by Emma Farge in Dakar; Editing by Mark Heinrich)