The FBI will join Lebanese and international investigators in a probe into last week’s massive Beirut explosion that killed at least 172 people, a senior US diplomat said on Thursday.

US Undersecretary for Political Affairs David Hale said in Beirut this was at the invitation of Lebanese authorities, Reuters reports.

The No. 3 US diplomat headed to Lebanon to stress the “urgent need” for the country to embrace fundamental reform, the State Department said. The visit comes in the aftermath of a blast that caused large-scale damage in the capital Beirut.