US Acting Defense Secretary Patrick Shanahan has canceled a trip to Europe to stay on top of the crisis in Venezuela and events at the US-Mexico border, the Pentagon said Wednesday.

The Pentagon on Wednesday appeared to downplay any active planning to directly intervene in Venezuela to topple President Nicolas Maduro, telling Congress it had not been given orders to prepare for war and stressing support for diplomacy.

The Pentagon said on Friday that it expected to send about 300 additional troops to the border with Mexico including roughly 100 cooks who would hand out meals, breaking with past policy to avoid troops coming in contact with migrants.

Acting Pentagon chief Patrick Shanahan has authorized $1 billion to build part of the wall sought by Donald Trump along the US-Mexico border, the first funds designated for the project under the president's emergency declaration.

Now that the Islamic State group has officially lost its geographic "caliphate," the Pentagon is marking a historic moment in its years-long campaign to defeat the jihadists.

Turkish Defence Minister Hulusi Akar told Pentagon officials during a visit to the United States that there must not be a vacuum of power during the withdrawal of US forces from Syria, state-owned Anadolu news agency reported on Saturday.

The acting US Secretary of Defence Patrick Shanahan arrived in the Afghan capital for an unannounced visit on Monday, meeting with top officials from NATO and the government.

Acting Pentagon chief Patrick Shanahan arrived in Afghanistan on an unannounced visit Monday as the United States leads a push for peace talks with the Taliban.

The Pentagon has identified about 7,000 troops that could be deployed to the border with Mexico if needed, a US official told Reuters on Wednesday.

The Pentagon grounded the global fleet of F-35 stealth fighters on Thursday, as a result of the first ever crash of the costliest plane in history.

US Defense Secretary Jim Mattis was not caught off guard by President Donald Trump's announcement that he was suspending military exercises with South Korea, a Pentagon spokeswoman said on Tuesday, adding he was consulted ahead of time.

President Donald Trump has ordered the Pentagon to prepare options for reducing the number of US troops in South Korea, the New York Times reported on Thursday, citing several people briefed on the deliberations.