How do you build a graph from a data frame using the igraph package?

Any way to build a graph ( igraph package ) from a Data Frame in R ?

The data frame contains node relationships.

    df = data.frame ( 
A = c("Berlin", "Amsterdam", "New York") , 
B = c("Munich", "Utrecht", "Chicago") 
) 

Edges are :

Berlin -> Munich
Amsteram -> Utrecht
New York -> Chicago