Thousands of Tunisians have marched through their capital, calling for the government to resign as the nation's political crisis deepens.

Saturday's march was the culmination of a week of protests organised by a coalition of opposition groups known as the National Salvation Front (NSF), calling for the resignation of the government and the dissolution of the assembly elected in 2011 to write the constitution.

It attracted fewer people than two similar protests held earlier this month - 10,000, according to police estimates.

The assassination of an opposition politician in July, the second in six months, has sharply polarised the country and prompted a walkout by about 60 opposition assembly members.

The powerful UGTT trade union, which has been mediating talks between the government and the NSF, on Saturday presented the government's latest proposals on resolving the crisis.

But after the meeting, Hamma Hammami, a representative of the opposition, said the group had replied to the ruling coalition's proposals and that "the key to ending the crisis is in the [government's] hands".

'Government must fall'

Hammami refused to elaborate on the proposals, except to confirm reports that they envisaged a change of government by September 29 at the latest, after a month of national dialogue on the new cabinet and the future constitution.

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But the NSF, a wide umbrella group of opposition parties, has repeatedly demanded the immediate resignation of the governing coalition, led by the moderate Islamist movement Ennahda.

It has refused to engage in any national dialogue until a non-partisan cabinet has been formed.

Tunisians overthrew their president in January 2011, kicking off pro-democracy demonstrations of the Arab Spring around the region and beginning a difficult transition to democracy.

"The government must fall," chanted the crowd that marched about 3km from the parliament building to the seat of the government in the centre of the city known as the Kasbah.

The opposition accuses the government of failing to ensure security in the country or improve the economy.

"Ali Larayedh, the Tunisian people will not be humiliated," they said, addressing the prime minister, who is part of Ennahda.

Source: Agencies