[R] multivariate lme or lmer?

[François Lefevre]

How can we get variance/covariance components in a linear model with 
random effects when the response is multivariate?
e.g. variance components estimates are obtained through lme or lmer in 
the univariate case but these functions do not seem to extend to the 
multivariate case. I'd like to estimate covariance components within or 
between levels of factors in a general case.
Sorry for this basic question and thank you for the help.
Francois