Amsterdam - A decision to evacuate, search and seal an entire Amsterdam shopping area Thursday was taken after what now appeared to be a dubious phone call by an anonymous informant warning of a terrorist attack, it emerged Friday.

Five of the seven people arrested Thursday on suspicion of plotting a terrorist attack at the mall were released on Friday, the Dutch Justice ministry said.

Two suspects remained in police detention - one suspected not of terrorist activities but other crimes, police said.

The Dutch Justice ministry said that after interrogations and home searches, no evidence had been found to suspect the five of terrorist activities.

Amsterdam's public prosecutor told reporters the investigation had now shifted from the seven arrested Thursday to the anonymous informant.

Meanwhile the Spanish ministry of interior affairs confirmed to Spanish media that one of the people arrested on Thursday was related to Moroccan Jamal Ahmidan - the man also known as El Chino who was involved in the Madrid train attacks of 2004 which killed 191 persons and left 1,800 people injured.

It was not known whether Ahmidan's relative was among the two who remained in police custody.

On Thursday the Dutch police arrested seven Dutch-Moroccan citizens aged 19 to 64 after the informant warned of a possible terrorist attack at the Arena shopping centre in south-east Amsterdam.

The call was made from a pre-paid phone that was later traced to Brussels.

The informant gave the police names, addresses and specific sites where the attacks would be planned. He said three explosives had been put in the shopping area, among others in the IKEA megastore.

On Thursday afternoon the entire shopping area, next to the Ajax football stadium, was evacuated, searched and sealed off.

Amsterdam mayor Job Cohen later told reporters: "The information we received was very specific. We did not want to risk endangering the lives of people shopping in the area." (dpa)