Police confirmed on Friday that attacks had been made on a Credit Suisse branch in the upmarket residential area of Hottingen and a postbox in the lakeside suburb of Rueschlikon in the early hours of Thursday morning.

Credit Suisse confirmed a security window of its branch had been shattered. Police said the damage, caused by an unidentified explosive device, amounted to several thousand francs.

A spokesman for Zurich police said investigations were continuing into who was behind the attacks and what had caused the explosions, while Glencore confirmed an incident had taken place on the property of CEO Ivan Glasenberg.

No-one was injured in either attack.

An unnamed group posted a letter on the indymedia.ch website claiming responsibility for the attacks. The letter said the group had targeted Credit Suisse and Glasenberg due to their support of the WEF.

In the letter, the activists criticised poor working conditions at Glencore and said it had targeted Credit Suisse for a host of reasons, including food price speculation, mass job losses and "betting against the Greek people".

Glencore's 2011 stock market flotation has led to increased scrutiny by environmental and anti-corruption campaigners over its involvement in mining operations in countries from Zambia to Colombia.

Until the listing, Glasenberg, who grew up in South Africa and became CEO in 2002, had lived with his family in relative anonymity in Rueschlikon, a lakeside town about 6 km from Zurich where he moved in 1994.

In 2011, left-wing activists claimed responsibility for a small explosion that broke windows at a hotel in Davos without hurting anybody.

At the time, a group calling itself Revolutionary Perspective said in a statement on an activist website it had targeted the ski resort's luxury Posthotel with a fire bomb as Swiss ministers and representatives of top bank UBS were staying there.