USA's Acting Secretary of Defense, Mark Esper, arrives for his first day in his new position at the Pentagon in Washington, DC, June 24, 2019. - Esper, who served in its much-heralded 101st Airborne Division, will bring the soldiering experience to the Department of Defense that former acting chief Patrick Shanahan lacked. (Photo by SAUL LOEB / AFP)
The US's Defence Secretary Mark Esper arrived in Saudi Arabia on Monday. AFP 

US and Turkey defence chiefs discuss Syria 'security mechanism'