* Police minister says expects arrests "within hours"
* AMCU leader says strikers' resolve not broken
* Four miners have been murdered in recent days
* Spot platinum hits 2-month high (adds police minister comments, Lonmin comment)
By Zandi Shabalala
MARIKANA, South Africa, May 14 (Reuters) - South Africa's police minister vowed to crack down on violence against platinum miners who were trying to return to work and arrest "within hours" strikers he said were behind a campaign of intimidation.
South Africa's longest and costliest strike ever, has taken a violent turn in recent days, with four miners killed as more employees try to report for work at the world's top platinum producers.
Earlier on Wednesday, striking members of the main Association of Mineworkers and Construction Union (AMCU) prevented other workers from returning to platinum producer Lonmin's shafts, thwarting the company's efforts to end the 16-week strike.
"In South Africa, the rule of law reigns ... Anarchy is not what is going to be accepted," minister Nathi Mthethwa told a news conference later.
Anglo American Platinum and Impala Platinum have also been hit by the strike, which has brought to a halt 40 percent of global production of the precious metal used for catalytic-converters in automobiles.
Lonmin had been aiming on Wednesday for a "mass return" of workers but a spokesman said "a very low number" had showed up. The producers have said many of the strikers have signalled a willingness to accept the latest pay.
Implats' mines around the platinum belt town of Rustenburg remain shut while it tallies the results of votes on its pay offer and assesses the security situation.
AMCU's arch-rival the National Union of Mineworkers (NUM) said its members were unable to return to work because of AMCU intimidation.
The charismatic president of AMCU, Joseph Mathunjwa, urged his members to stay the course.
"Let's stay strong. Yes it's difficult, but let's hold each other by the hand and stay strong. Onward!" Mathunjwa told thousands of strikers at a rally near Lonmin's Marikana mine.
The strikers, many wielding sticks, roared their approval to Mathunjwa's remarks at the rally held near the site where police shot dead 34 striking Lonmin miners in August 2012. That sent spot platinum to two-month highs over $1,470 an ounce.
Mathunjwa, a Salvation Army lay preacher who often evokes both God and class warfare, used typically combative language, telling the crowd that "the purpose of capital is to destroy AMCU and its members."
The companies decided to take their latest wage offer directly to AMCU's members after wage talks with the union collapsed three weeks ago.
Mathunjwa said AMCU was going to the labour court next week to prevent the firms from by-passing the union in this way.
The companies said they would "strongly oppose" this, saying in a statement that they "wanted to ensure that employees are fully informed of the offer, and that they are empowered to accept or reject the offer of their own free will."
The industry has long accused AMCU of using intimidation to keep its members in line, allegations it denies.
The companies are offering increases of up to 10 percent that they say would raise the overall minimum pay package to 12,500 rand ($1,200) a month by July 2017, including cash allowances such as for housing.
They say they can go no higher given rising costs and depressed prices and Lonmin's chief executive Ben Magara said on Monday restructuring and job cuts were inevitable as it posted a steep fall in six-month earnings.
Platinum's price, despite Wednesday's moves, has largely taken a muted response to the stoppage as traders have bet there are sufficient above-ground stocks to meet demand which remains far from robust.
AMCU had initially demanded an immediate increase to 12,500 rand in the basic wage, excluding allowances, but softened that in March to staggered increases that would amount to 12,500 rand within three or four years - still a third more than what the companies are offering in basic salaries.
The strike highlights the discontent among black miners who feel they are still not reaping the benefits of the country's mineral wealth two decades after apartheid ended.
It has also hurt already sluggish growth in Africa's most advanced economy and rating agency Moody's said on Wednesday the country's credit rating remained under pressure. (Additional reporting by Ed Cropley and Tiisetso Motsoeneng in Johannesburg; Writing by Ed Stoddard; Editing by Mark Potter and Elaine Hardcastle)