Multiple directional ribs igraph

Question

I would like to express the edges between vertices 1 and 2 in the following graph as two separate edges with arrows in opposite directions.

require(igraph) 
e <-  c(1,2, 2,3, 3,1, 3,4 , 4,1 , 2,1)
g <- graph(e, n=5, directed = TRUE)
tkplot(g, layout=layout.circle )

I get only one edge with an arrow at both ends. It should be easy, but I have not found it anywhere and can not understand. Any ideas?