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Bahrain is at a tipping point. By inviting in 1,500 Saudi and Emirati troops to help restore order the ruling al-Khalifa family have dramatically raised the stakes in the tiny Gulf kingdom.

It is a controversial and somewhat desperate measure as Bahrain's own police and security forces have shown themselves patently incapable of handling the anti-government protests to date.

It follows a series of behind-closed-doors conversations between key figures in each of those countries on how to contain the crisis.

This has resulted in what Gulf rulers would like to present as almost an "internal family matter", with one or other fraternal country helping out another. In practice, it is unprecedented and potentially highly inflammatory. So how has it gone down with the various interested parties?

Opposition leaders have been quick to condemn this variously as "an invasion", "an occupation", and "an act of war". The protesters fear they will now be subject to excessive violence by foreign troops. They do not accept the government's premise that the troops have been called in to guard key sites like oil storage depots, pointing out that they have not attacked those.

Social networking sites like Twitter and Facebook have been blazing with angry comments like this one on Tuesday: "Is it fair to say the first war ever waged in Bahrain's history was against its own peaceful citizens?"

The ruling al-Khalifa family and state media have put out a number of statements saying this was a necessary measure to restore law and order.

The night before the Saudi troops went in, a government official told the ´óÏó´«Ã½: "The situation needs to be stabilised as this is getting out of control. Hopefully rule of law can be enforced and talks [with opposition leaders] can get under way."

There is almost certainly a divergence of views within the ruling family. After seven protesters were killed last month, it was the crown prince's personal intervention that led to security forces being withdrawn, and a search for dialogue and compromise intensified.

But there are others within the family who take a tougher line, fearing that unless these protests are put down ruthlessly their entire dynasty could be at stake.

A number of analysts believe that Bahrain had little choice but to invite in Saudi troops, with Saudi Arabia's authoritarian rulers adamant that the unrest had to be stopped before it spilled over into Saudi's Shia-dominated and oil-producing Eastern Province.

There has been some minor unrest there already but nothing compared to what could erupt if neighbouring Bahrain saw a full-scale Shia revolution. Saudi Arabia is Bahrain's closest Gulf ally and the two countries frequently act in concert.

Iran has called the deployment of Saudi troops to Bahrain "unacceptable". Bahrain has responded by effectively saying "mind your own business" and has withdrawn its ambassador to Tehran in protest. The Bahraini government has long suspected Iran of trying to foment a "fifth column" of subversives in Bahrain, but its critics say this is just an excuse to round up its domestic opponents.

While many Bahrainis have been appalled and alarmed at the arrival of foreign troops, others, perhaps bizarrely, have breathed a sigh of relief. They are hoping it will spell an end to the protesters' illegal and sometimes intimidating checkpoints that have sprung up around the country, paralysing business and choking off the economy.

Bahrainis complain of gangs of local Shia youths manning these checkpoints, demanding to see people's ID cards, and turning back anyone who is from the Sunni minority.

This, however, pales next to the mounting reports of horrific casualties suffered by protesters as they are brought into hospitals.

Many want nothing more than an elected parliament with full executive powers but others are being radicalised by the violence into demanding the departure of the king and perhaps the entire ruling family.