Election observers working for the European Union (EU) say some voting results have been doctored in Mozambique, as unrest in the country continues to grow.

Thousands of people joined opposition protests on Monday that were called by independent presidential candidate Venâncio Mondlane.

He blames security forces for gunning down his lawyer Elvino Dias and another political official called Paulo Guambe in the same car last Friday - but they deny any wrongdoing.

Official results from the general election held on 9 October are due to announced by Friday.

Evidence has been found of "irregularities during counting and unjustified alteration of election results at polling station and district level", said the EU observer mission in a statement on Tuesday.

It is now urging "the electoral bodies to conduct the tabulation process in a transparent and credible manner, ensuring the traceability of polling station results".

Vote-buying, inflated voter rolls in strongholds of the governing Frelimo party and voter intimidation have all been reported by the US-based International Republican Institute, which also sent a multinational election observer mission to the southern African nation.

Mozambique's national results are meant to be published on the electoral commission's website for all to see, but last month the body said its website had suffered a cyber-attack. The website remains inactive.

Fifty-year-old presidential hopeful Venâncio Mondlane, who has the backing of opposition party Podemos, has already claimed victory and alleges that the killing of his aides on Friday night was politically motivated.

"This was a crime committed by the defence and security forces. There's no doubt about it. The special forces killed Elvino [Dias]," he has said.

Mondlane rallied people in cities across Mozambique to protest against the killings and against what he says is the theft of the election.

On Monday, police used live rounds, tear gas, armoured vehicles and police dogs to push back protesters from the site in the capital city Maputo where Dias and Guambe were shot dead.

Demonstrators also blocked roads with burning tyres and barricades.

Footage shows Mondlane, and journalists running for cover after shots were fired in their direction.

Across the cities of Maputo, Beira and Nampula, local media reported that there were multiple arrests and at least 16 people were wounded and taken to hospital.

Shops and businesses closed on Monday but began reopening their doors on Tuesday.

The funeral for Dias is set to take place on Wednesday. Mondlane has called for further protests on Thursday and Friday.

There is growing pressure on the Mozambican authorities to identify the killers and bring them to justice following strong condemnation from former Mozambican President Armando Guebuza, the African Union, the UN, the US and the EU.

Celebrated Mozambican author Mia Couto has called the killings a "crime against the nation".

Mozambique has only ever been governed by one party - Frelimo - which has ruled since independence from Portugal.

The country is guaranteed a new president because President Filipe Nyusi is stepping down after serving the two-term limit.

The Frelimo candidate is 47-year-old Daniel Chapo.

His rivals in this election are Mondlane, Ossufo Momade - the former rebel commander-turned-leader of the main opposition party Renamo - and Lutero Simango from the Mozambique Democratic Movement.