Malaysia on Sunday said that recent fuel price rises had not deterred the smuggling of diesel into Thailand and vowed a clampdown.

Domestic Trade and Consumer Affairs Minister Shafie Apdal said monitoring the smuggling was difficult since many Thais were crossing over as tourists into neighbouring Malaysia.

"We cannot stop them from pumping petrol or diesel for their vehicles because they enter the country as tourists but if there are abnormalities in their entries, we will monitor," Shafie was quoted as saying by the official Bernama news agency.

Shafie said his ministry would post more enforcement personnel on the border, including in territorial waters.

"If in our territorial waters, we will seek help from the navy and marine police," he said.

"We have detected cases of fishermen abusing their fishing boats to sell diesel at mid-sea," he added.

Cutting subsidies

Malaysia raised the price of petrol by 6.6 percent and diesel by 18.5 percent in July, bringing the price of diesel to RM1.281 a litre.

The government said the increases, the fourth since October, were part of efforts to cut the soaring cost of its fuel subsidies amid record high global crude oil prices.

Despite the rises, prices are still low compared with the rest of the region. Only the oil-rich kingdom of Brunei has prices lower than Malaysia's.

The diesel subsidies have tempted smugglers to sell the fuel in neighbouring Thailand where it is more expensive, or pass it on to industrial users not entitled to the subsidy.

Subsidies for petroleum cost Malaysia RM4.8 billion last year. The government has said subsidies are expected to reach RM6.63 billion this year due to rising oil prices.