ISIS suspected in border killings

• Suspected ISIS militants killed 16 Iraqi border guards, official says


• Official: Four others in critical condition


• Base is only one with Syria that is still controlled by Iraqi forces

Baghdad, Iraq (CNN) -- An attack by suspected ISIS militants on a border guard base near the Syrian border left at least 16 killed and four others seriously wounded according to Faleh al-Issawi, the deputy head of the Anbar provincial council in Iraq.

The militants slaughtered the 16 border guards, including their commanding officer, in a surprise early morning attack on Monday, al-Issawi said.

Four others are in critical condition, he said.

The base attacked is near al-Waleed border crossing, the only crossing Iraq has with Syria that is still controlled by Iraqi forces. ISIS maintains control of almost all of Anbar -- Iraq's largest province.