At least four people were murdered in Sweden today in yet another terror attack in which a vehicle was used to mow down pedestrians.

The head of the World Council of Churches, general secretary, Rev Olav Fykse Tveit,  denounced the Stockholm attack and mourned the loss of life, extending prayers for the victims and their families and friends.

A lorry was driven into a store in central Stockholm, killing at least three people and injuring a number of others. Unconfirmed reports have also emerged of a secondary incident - a shooting - in a separate area of the city but the two incidents are not believed to be related.

The incident occurred on Drottninggatan, one of the city's major pedestrian streets, just before 15:00 local time. Swedish police said they are treating it as terrorism.

Witnesses said they saw a truck drive into the front window of the Ahlens department store. They had seen people on the ground. Stockholm's Parliament was evacuated and the area cordoned off.

'Once again, people going about their daily lives, in celebration of holidays, have suffered a violent attack,' said Tveit. 'We must join together, not just to condemn these actions but to strengthen our pursuit of just peace, and to strengthen our resolve not to allow extremist violence to separate us from each other.'

Tveit called for prayers and solidarity with the people of Sweden. He said, 'Sweden is a country that has taken so many peace initiatives in other parts of the world, but now is hit by these inhuman actions of terror in the middle of their capital of Stockholm.

'We pray for the victims and their families, and we seek God's mercy, love and grace that we may be empowered with strength to continue our pilgrimage of justice and peace.'

Almost immediately, #PrayforStockholm began trending on Twitter, with inevitable comparisons between this and what happened in London just two weeks ago.

'Sweden has been attacked. Everything points to the fact that this is a terrorist attack,' said Prime Minister Stefan Lofven.

There was no immediate claim of responsibility.

Al Qaeda in 2010 urged its followers to use trucks as a weapon.

In London on March 22, a man in a car plowed into pedestrians on Westminster Bridge, killing three, and then stabbed a policeman to death before being shot by police. A fifth victim, the Romanian woman who was forced into the River Thames by the attacker's rented car, died in hospital this week.

Islamic State claimed responsibility for both an attack in Nice, France, last July, when a truck killed 86 people celebrating Bastille Day, and one in Berlin in December, when a truck smashed through a Christmas market, killing 12 people.

 Additional reporting by Reuters