R言語を始めたばかりです。
RStudioなどをいれ、グラフのプロットを確認するとこまできました。igraphを使いたく、

install.packages("igraph")
と未保存のスクリプトに書いたのですが、うまくインストールされません。

R version 3.6.0 (2019-04-26) -- "Planting of a Tree"
Copyright (C) 2019 The R Foundation for Statistical Computing
Platform: x86_64-w64-mingw32/x64 (64-bit)

R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.

R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.

Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> install.packages("igraph")
WARNING: Rtools is required to build R packages but is not currently installed. Please download and install the appropriate version of Rtools before proceeding:

https://cran.rstudio.com/bin/windows/Rtools/
also installing the dependencies ‘magrittr’, ‘pkgconfig’

trying URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/magrittr_1.5.zip'
Warning in install.packages :
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/magrittr_1.5.zip': HTTP status was '404 Not Found'
Error in download.file(url, destfile, method, mode = "wb", ...) : 
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/magrittr_1.5.zip'
Warning in install.packages :
  download of package ‘magrittr’ failed
trying URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/pkgconfig_2.0.2.zip'
Warning in install.packages :
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/pkgconfig_2.0.2.zip': HTTP status was '404 Not Found'
Error in download.file(url, destfile, method, mode = "wb", ...) : 
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/pkgconfig_2.0.2.zip'
Warning in install.packages :
  download of package ‘pkgconfig’ failed
trying URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/igraph_1.2.4.1.zip'
Warning in install.packages :
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/igraph_1.2.4.1.zip': HTTP status was '404 Not Found'
Error in download.file(url, destfile, method, mode = "wb", ...) : 
  cannot open URL 'https://cran.rstudio.com/bin/windows/contrib/3.6/igraph_1.2.4.1.zip'
Warning in install.packages :
  download of package ‘igraph’ failed
>

いろいろ調べたのですが、結局よくわからなかったので質問させていただきました。
ご指導ご鞭撻のほどお願いいたします。