* Market volatile as buying activity jumps - traders
* Indo SIR20 rises as much as $1.49/kg, producers anticipate $1.50/kg
* Futures underpinned by producer efforts to boost prices
By Anuradha Raghu
KUALA LUMPUR, April 30 (Reuters) - Prices for rubber cargoes in Asia rose this week after key producers announced plans to boost prices by curbing output and lifting premiums sharply over the market benchmark, traders said on Thursday.
At least 10 key rubber producers in Asia, where most of the world's rubber is grown, last week said they would hike prices sharply from the second half of 2015, ditching a system of pegging them near the benchmark set by the Singapore SICOM exchange.
The most active rubber contract on the Shanghai futures exchange for September delivery climbed to as much as 14,580 yuan per tonne this week, the highest since August last year, as investors increased long positions in anticipation of the plan.
The contract posted its biggest monthly gain in April since December 2010, with a 14 percent rise.
Benchmark TOCOM rubber futures meanwhile edged higher to 218.6 yen on Thursday on top producers' efforts to boost prices, but profit-taking after a surge to a seven-week high earlier this week capped gains.
"There has been volatile movement this week. Prices are definitely firmer," said Singapore-based trader. "Overall, buying activity has picked up but magnitude-wise, it's hard to gauge."
"The change of sentiment has caused some people to either take speculative positions or to cover their shorts. But whether there's really long-term positions because of need, or just speculations, it's hard to say," the trader added.
July shipments for the Indonesian SIR20 grade was traded as high as $1.49 per kg compared with $1.43-1/2 a week ago, with buying interest coming in Thai-based tiremakers, dealers said.
Rubber producers in Indonesia, the world's second-biggest grower after Thailand, are pinning hopes for prices to reach $1.50/kg. They are also reluctant to sell with some areas experiencing raw material shortages due to the wintering season.
"If they do not have the raw material in hand, they prefer not to sell forward," said a trader in Jakarta.
Thailand's STR20 exchanged hands between $1.46 and 1.47 a kg for the July delivery, firmer than last week as Chinese buyers and major tiremakers snapped up cargoes, said a trader from the southern Thai city of Hat Yai.
The Thai tire-grade RSS3 was sold between a range of $1.76 and 1.77 per kg.
Tiremakers also bought the Malaysian SMR20 grade for $1.50 for the June and July delivery, traders said.
The main SICOM contract touched a high of 150 U.S. cents a kg, the highest since January. (Editing by Anand Basu)