BANGKOK- Hundreds of freight trucks deliberately clogged a major thoroughfare of Thailand's notoriously congested capital on Tuesday, seeking to pressure the government into lowering diesel prices.

Police tried unsuccessfully to shift the protesting trucks and taxi drivers as they crawled along the main northbound highway out of Bangkok, some carrying banners demanding the energy minister's resignation for failing to make fuel affordable.

"We have asked the government to fix the fuel price problem many times, but nothing happened," said Apichart Prairungruang, chairman of the Land Transport Federation of Thailand.

"The government has never responded to our demands... From now on, we will pressure the government with a bigger group."

The federation wants the price for a litre of diesel capped at 25 baht ($0.76), lower than the 30 baht per litre cap the energy ministry has maintained since October.

It says the real price is 35 baht per litre, which reflects the rise in prices globally.

Ministry spokesperson Sompop Pattanariyankool said truck drivers' demands would require 18 billion baht ($546.8 million) per month in state subsidies, which "cannot be done".

Khomdet Jumpaman, who drove 700 km (435 miles) from the northern province of Chiang Mai, said he was struggling and had fewer customers because of his increased transportation costs.

"We have to give up our profit to cover the fuel cost, so I'm here asking the government to help."

($1 = 32.9200 baht)

(Additional reporting by Pararat Thepgumpanat; Writing by Martin Petty; Editing by Alexandra Hudson) ((; +66896070413))