Syrian authorities have halted payments to French oil major Total for its oil production activities in the troubled country, a spokesman for the company said on Friday.

This is a further indication that U.S. and European Union sanctions imposed in response to President Bashar al-Assad's crackdown on dissent are starting to bite.

Syria's oil exports worth $400 million a month in total are at a standstill.

"We are not paid by the Syrian government any longer," a spokesman for Total said, adding the group had observed a slight production fall in the country.

Syrian oil represents less than 1 per cent of daily global production but accounts for a vital portion of Syrian government earnings, which Western powers say Assad can use for a bloody military crackdown on the opposition.

Authorities have stopped payment to oil companies towards the end of September, one source with knowledge of the situation said.

The sanctions aimed at crude oil exports have warded off normal buyers of Syrian crude, which mainly flowed to Europe, causing storage tanks to brim and forcing cuts.

Syria produced around 350,000 barrels per day (bpd) before the unrest of which about a third was exported, with most flows going to Europe.

Gulfsands Petroleum, which produces more than 90 per cent of its total output from Syria, said on Thursday the Syrian government would resume payments to the company for oil if exports resumed.

In a further sign that foreign interests could be jeopardised, the EU is mulling tougher sanctions on Syria which would make it illegal for international firms to maintain oil and gas investments there.

Total produces 39,000 barrels per day of oil equivalent in the country.