Rmarkdown : can we merge two cells with kableExtra?

Is there a way to merge two cells with kableExtra when knitting from Rmarkdown to HTML?

bbb = 5aaa = data.frame(matrix(c(1,2,3,4, paste(bbb),""), nrow = 2, byrow = T))aaa

I want the value bbb (the value of the merged cells varies) to appear in the middle of the last two columns when applying kable(aaa) %>% kableExtra(...)

> aaa  X1 X2 X31  1  2  32  4  5

Any suggestion ? Thanks :-)