Washington: The US State Department’s third-ranking official, Tom Shannon, is stepping down from his post, the department said on Thursday, becoming the latest senior diplomat to exit since President Donald Trump took office a year ago.

Shannon, who serves as under secretary of state for political affairs, is the top US career diplomat and has been a fixture among the nation’s diplomatic ranks during more than 34 years of service. In a letter to department staff, Shannon, 60, said he was resigning for personal reasons.

State Department spokeswoman Heather Nauert said Shannon agreed to Secretary of State Rex Tillerson’s request that he stay on until his successor is named. Nauert said Shannon had served under six presidents and 10 secretaries of state.

‘My decision is personal, and driven by a desire to attend to my family, take stock of my life, and set a new direction for my remaining years,’ Shannon wrote.

Shannon’s departure is part of a steady stream of senior career diplomatic officers who have left since Trump became president. It will deprive the State Department of a seasoned veteran at a time of pressing diplomatic concerns including the threat posed by a nuclear-armed North Korea.

Tillerson in November said he was offended by claims that the State Department was being hollowed out under Trump, saying it was functioning well despite scathing criticism from former American diplomats including Nicholas Burns and Ryan Crocker.

The forcing out of many senior diplomats, the failure to nominate or to win Senate confirmation for officials to fill key agency roles, and a perception that Tillerson is inaccessible have eroded morale, according to current officials.

Trump kept Shannon on board when he assumed the presidency and must now appoint a successor who would need Senate confirmation.

Under Secretary of State Steve Goldstein denied that Shannon’s departure was related to low morale at the State Department.

‘Tom Shannon is an amazing man. He has done an incredible job on behalf of the secretary and the country,’ Goldstein told reporters, adding that Shannon had informed Tillerson of his decision on Wednesday.