Athens is preparing to welcome German Chancellor Angela Merkel on Friday afternoon in the wake of Greece's return to international bond markets on Thursday for the first time in four years.

Following the successful sale of five-year bonds at 4.75 percent, which exceeded all expectations, the Greek government expects a strong message of support from the German leader for the recovery efforts of Greece, which was once pushed to the brink of bankruptcy in a severe debt crisis.

It will be Merkel's second visit to Athens since the start of the crisis. As it happened in autumn 2012, police has taken tight security measures.

The security is particularly heavy after a strong bomb blast hit the headquarters of the central Bank of Greece in the heart of the Greek capital on Thursday morning, causing damage but no injuries.

Approximately 5,000 police officers have been deployed across the city centre. Roads will be closed to traffic and all rallies have been banned during the German leader's visit, which will last about five hours.

Despite the ban, opposition parties and trade unions have called on Greek citizens to participate in anti-austerity protests in central squares.

Some Greeks blame Merkel's insistence on harsh fiscal adjustment for the pains they have suffered in recent years.