Bahrain riot police fired tear gas and stun grenades at anti-government activists on Thursday and members of the Force India race team were caught up in a petrol bomb incident as unrest simmered ahead of this weekend's Formula One Grand Prix.
Protesters seeking to oust Bahrain's monarchy have threatened "days of rage" to coincide with the race, while organisers have ignored appeals to call off an event that was cancelled last year due to violent demonstrations during the Arab Spring.
While international sports correspondents are in Bahrain for the race, non-sports reporters from Reuters and some other news organisations have not been granted visas to visit the Gulf island.
Several hundred people tried to stage a protest in the capital, Manama, on Thursday. The protesters moved from a Shi'ite neighbourhood in the back streets chanting slogans against the government but riot police fired tear gas and stun grenades when they tried to enter a main highway near the British embassy.
Bahrain's chief of public security said a number of "rioters and vandals" had been arrested for taking part in unlawful protests.
Bahrain has been in turmoil since a democracy movement erupted more than a year ago after uprisings in Egypt and Tunisia. Protests were initially crushed with the loss of dozens of lives but youths still clash with riot police and thousands take part in opposition rallies.
Western companies are opting not to entertain clients and partners at the race following calls for sponsors to boycott the event because of the political turmoil.
Shell, which sponsors the Ferrari team, will not be hosting any guests at the event, a source familiar with the company's plans said.
For Bahrain's al-Khalifa family - a Sunni Muslim dynasty ruling a majority Shi'ite population and caught between powerful neighbours Saudi Arabia and Iran - this year's race has been an opportunity to tell the world that all is back to normal.
But with demonstrations taking place daily, two members of the British-based Force India team asked to go home after the petrol bomb scare.
The Bahrain race circuit said four members of the team travelling between the track and the capital, Manama, drove through "an isolated incident involving a handful of illegal protesters acting violently towards police".
"During this incident a Molotov cocktail landed in the vicinity of their vehicle," a statement said.
Force India, whose drivers are Germany's Nico Hulkenberg and Britain's Paul Di Resta, said they had not been a target of the violence and no one in the team was hurt.
"It is obviously not right that sort of stuff happens," Hulkenberg said. "We are here to race. The F1 business is about entertainment and these sort of things should not really be happening to us."
A day before the Formula One cars appear on the track for practice sessions, there were signs of nervousness among race teams. The MRS team, entered in the supporting Porsche SuperCup series, withdrew its entry from the weekend season-opener, citing safety reasons, without travelling to Bahrain.
Red Bull's double world champion Sebastian Vettel played down the unrest. "I haven't seen anyone throwing bombs. I don't think it's that bad. I think it's a lot of hype."
"I think it's not a big problem and I think I'm happy once we start testing tomorrow because then we worry about the stuff that really matters - tyre temperatures, cars," added the 24-year-old German.
Overnight, police trying to suppress protests in the Shi'ite village of Sanabis fired tear gas and shotguns to disperse hundreds of demonstrators, a Reuters photographer said.
They were chanting anti-government slogans such as "The people want the fall of the regime!" and "Down, down Hamad!" referring to the ruler, King Hamad.
"A number of rioters and vandals had been arrested for taking part in illegal rallies and gatherings, blocking roads and endangering people's lives by attacking them with petrol bombs, iron rods and stones," the Information Affairs Authority said in a statement, citing Major-General Tariq Al Hassan.
A precise number of arrests was not given, but the opposition and human rights activists say that at least 90 people have been arrested so far this week.
Nabeel Rajab, founder of the Bahrain Centre for Human Rights, said holding the race showed a lack of respect for those hurt in the past year of protests.
"We are not against Formula One because we are against Formula One - every part of our nation likes to enjoy this sport. We are against rewarding dictators. Formula One in Bahrain has been taken as PR for the ruling elite, the repressive dictators who are ruling the country," he said.
Manama has been blanketed with security, with police stationed on the various bridges linking the capital to the rest of the country and the Bahrain International Circuit in Sakhir, where the Grand Prix will take place.
Politics aside, considerable sums of money are stake this weekend. Last year, Bahrain paid a "hosting fee" of $40 million despite cancelling the race. The Bahrain race drew 100,000 visitors to the nation of just 1.3 million and generated half a billion dollars in spending when it was last held two years ago.
A group of British lawmakers warned Formula One sponsors that they risk damaging their brands by supporting the Bahrain Grand Prix and said the race should have been called off.
Andy Slaughter, who heads the All Party Parliamentary Group for Democracy in Bahrain, has written to several of the blue-chip companies who bankroll the sport.
"We are most alarmed that you see no grounds to sever your brand and save its reputation from a totalitarian regime," he added. "We sincerely hope you will rethink your associations with the Bahrain Grand Prix and decide to curtail your sponsorship of the race at Sakhir."
The letter was sent to Royal Dutch Shell, Vodafone, Unilever, Total, Siemens, Red Bull, UBS, News Corp, Hugo Boss, Ferrari, ExxonMobil, Deutsche Post and Daimler, Slaughter said.
Thomson Reuters, parent company of Reuters news agency, sponsors the Williams Formula One team but Slaughter did not include it on his list of firms that were sent the letter.
The race weekend comes as the Bahrain government must decide what to do about a jailed Shi'ite rights activist who is on hunger strike.
Abdulhadi al-Khawaja is one of 14 men in prison for leading the uprising last year. Releasing him would involve a loss of face for the government, but his death would create a martyr.
Bahrain is the base for the U.S. Navy's Fifth Fleet, among whose tasks is deterring Iran from making good on recent threats to disrupt Gulf oil tanker routes to the West. Washington has only gently prodded Bahrain's Saudi-allied rulers to improve human rights and push forward political reforms.
Thirty-five people were killed during the uprising last year, as well as security personnel.