RIYADH: In ultra-conservative Saudi Arabia, where the sexes are strictly segregated, traditional matchmakers face tough competition from blossoming marriage services on online social networks.

More than 200 Twitter sites and dozens of other forums on the Internet offer services for Saudi men and women seeking spouses, angering matchmakers like Um Sami who sees it as "organised prostitution."

"Social networks undermine our work and everything they offer is virtual: they use nicknames and they are not reliable," said Um Sami, an elderly woman and well-established matchmaker from the Red Sea city of Jeddah.

For her, many of these websites are "fraudulent" and some are even an organised form of prostitution.

"Marriage via online platforms is one hundred percent doomed to failure," she said, stressing that only her traditional matchmaking method can lead to a successful marriage.

For matchmakers like Um Sami the business has flourished by word of mouth.

Families ready to marry off their offsprings contact her with details about their children and provide pictures which she carries around with her on rounds to match candidates.

But her job is not a simple one because, as she says, there are many different types of weddings that can be contracted in Saudi Arabia, from the traditional unions to unconventional ones by Western standards such as the "misyar" marriage.

A misyar -- or "visitor's" marriage -- is one in which couples live separately but can meet up when they want, usually for sexual encounters.

It is allowed in Sunni-powerhouse Saudi Arabia but couples who choose to go that way will keep it a family secret shared only with the matchmaker.

In a traditional union sealed with the help of Um Sami, the bride and groom each pay the matchmaker around 2,000 riyals (530 dollars.

But the fee for a misyar wedding is much higher and usually starts around 5,000 riyals (1,300 dollars) -- with the man alone having to foot the bill while his spouse continues to live in her own home.

Misyar is often the marriage of choice for polygamous men as well as divorcees and widows in Saudi Arabia, where extra-marital relations are strictly banned and punishable under rigid Islamic laws.

A couple caught having sex out of wedlock in Saudi Arabia are sentenced to stoning and lashes, and unmarried couples who dare share a meal in a restaurant or spend time together alone risk being arrested.

Human rights activists and intellectuals have slammed misyar marriages as a form of "legalised adultery."

Offers to help seal both traditional marriages and misyars are rife on the Internet.

The website khtabh.net allows men and women to post their requests.

One message reads: "Misyar marriage wanted immediately in Riyadh... and the matchmaker or mediator will be offered a big reward."

Candidates are also asked to give personal details, including their marital status, monthly salary, education and a brief description of who they are and what they look like.

A man wanting to marry has posted a request on one such site for a "tender, quiet, good humoured and plump" wife.

A woman from Riyadh with special needs said she was 23 "pretty, blind, fair-skinned. Willing to marry a normal, non-smoking man even if he is polygamous as long as his first wife is informed."

Both online matchmaking sites in Saudi Arabia and matchmakers frown upon more unorthodox forms of marriage such as "misfar" and "misyaf" marriages for men who travel frequently or spend each summer abroad.

"There are so many offers which one finds tempting to try, but my friends have warned me against certain websites that can be traps," said 20-year-old Amjad Ismael.

Many online matchmaking services ask for a deposit upfront, he said.

Abu Mohammed, a 40-year-old who is already married and is looking for a second wife, said he has had a "bad experience" with online matchmakers.

"They are not serious. They try to take advantage of people contacting them, especially if they are married," he said. "I have now decided to go back to the traditional matchmaker to ensure confidentiality."

But younger people still prefer social networks as a tool to tie the knot "because they are an easy way to get to know each other," said sociologist Abu Bakr Baqdar.

"In the past, people got to know one another through families and neighbours," he said. Young people are now looking for "less traditional means to meet away from their families' interference."