Acting US defence secretary Patrick Shanahan has withdrawn from consideration for the post of Pentagon chief, making him the latest person to leave a senior White House position.

Mr Shanahan (56) was appointed to the position following the resignation of James Mattis last year. His departure was announced in a tweet by the president, Donald Trump, who said Mr Shanahan would not be going forward with his confirmation process to replace Mr Mattis permanently “so that he can devote more time to his family”.

His withdrawal was announced about an hour after USA Today reported the FBI was investigating a domestic violence incident nine years ago involving Mr Shanahan and his ex-wife as part of a background check ahead of an expected Senate confirmation hearing.

Mr Trump announced that secretary of the army, Mark Esper, would be the new acting secretary of defence. “I know Mark, and have no doubt he will do a fantastic job!” the president tweeted.

Iran situation

Mr Shanahan’s departure comes at a critical time given the escalating tensions between the US and Iran. On Monday, Mr Shanahan announced the deployment of an additional 1,000 US troops to the Middle East, in addition to the 1,500 extra military members announced last month.

He was seen in part as a counterweight to national security adviser John Bolton, who has taken a tough line on Iran and previously advocated bombing the country. However, Mr Bolton overruled the defence department on issues in recent months, such as the designation of Iran’s Islamic Revolutionary Guard Corps as a terrorist organisation, which Mr Shanahan opposed.

Mr Esper has been secretary of the army since November 2017. A graduate of the US military academy, he worked in the private sector as a lobbyist and on Capitol Hill before his appointment by Mr Trump.

Mr Trump’s first defence secretary, James Mattis, resigned from the administration last December following the president’s decision to withdraw US troops from Syria. In his resignation letter to Mr Trump, the retired marine general told the president he had the right to have a secretary of defence “whose views are better aligned with yours”.

Pervasive ‘acting’

Though Mr Shanahan was appointed as acting defence secretary in February, he was never officially nominated for the role, part of a pattern that has seen various positions filled by individuals on an “acting” basis. White House chief of staff Mick Mulvaney, for example, remains in an “acting” capacity, despite having replaced John Kelly six months ago.

The change of personnel at the Pentagon comes as relations between Washington and Tehran reach a fresh low, following an attack on two oil tankers last week. The United States has blamed Iran for the assault in the Gulf of Oman, prompting the Pentagon to deploy the extra troops to the region.

Despite US claims that video and other evidence proves that Iran was behind the incident, many allies have said they need more evidence.

EU foreign policy chief Federica Mogherini was in Washington on Tuesday for meetings with secretary of state Mike Pompeo, at which Iran was expected to top the agenda.