Sweden's left-wing opposition parties have widened their lead over the centre-right government ahead of September's general election, according to a new poll on Friday.

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The Synovate survey, published in the Dagens Nyheter daily, showed the three-party opposition had 49.6 percent of voter support, compared to 43 percent for the four-party governing coalition.

The latest poll indicates the opposition bloc is strengthening its lead after two other recent surveys gave it an advantage of between 1.4 and 4.3 percentage points over the government.

On an individual party level, the main opposition Social Democrats remain Sweden's most popular party, with 35.2 percent of voter support, while Prime Minister Fredrik Reinfeldt's Moderate Party garnered 27.7 percent backing.

Less than a year ago, several opinion polls showed a clear lead for the governing alliance, with approval ratings of up to 50 percent.

The government had won general approval for its handling of the financial crisis but has since been damaged by a series of controversies, including over a dramatic cut in the numbers eligible for long-term sick leave compensation.

Friday's poll also showed strong support for the far-right Sweden Democrats, which is not part of either bloc, with 5.6 percent of those questioned saying they would vote for the party.

If the party, which won 2.9 percent of the vote in 2006, achieves a similar result in the September 19 poll, it would win its first seat in parliament.

Under Sweden's electoral system, parties can only enter parliament if they obtain at least four percent of the overall national vote or more than 12 percent of the vote in an individual constituency.

Founded in 1988, the far-right party argues Sweden should remain a "homogeneous society" by drastically cutting the numbers of immigrants.

For Friday's poll, Synovate surveyed 2,712 people between February 8 and February 24.