BERLIN (AP): Nearly a year after former President Donald Trump ordered thousands of troops to leave Germany, capping a series of setbacks for US relations with major allies, US Defence Secretary Lloyd Austin began an inaugural tour of Europe to shore up partnerships that are a cornerstone of the post-World War II order.

Austin arrived in Berlin on Monday against the backdrop of a newly emerging crisis with Iran, which on Monday blamed Israel for a recent attack on its underground Natanz nuclear facility. Israel has not confirmed or denied involvement, but the attack nonetheless imperils ongoing talks in Europe over Tehran's tattered nuclear deal.

Also at stake in Austin's visit is the future direction of US defence commitments in Europe at a time of growing concern about Russian military intervention on NATO's periphery, including a build-up of Russian forces near Ukraine's border.

US Secretary of State Antony Blinken was headed to Europe to discuss with US allies the Ukraine situation as well as the administration's thinking on further withdrawals of troops from Afghanistan.

The United States also seeks European support for its approach to countering China around the world and for efforts to restore an international agreement with limits on Iran's nuclear programme.

Austin arrived in the German capital on Monday night and held talks Tuesday with senior government officials, including German Defence Minister Annegret Kramp-Karrenbauer. He announced he would be expanding the US military presence in Germany by 500 troops and had stopped planning for large-scale troop cuts ordered by the Trump administration.

He will also visit NATO headquarters later this week in Belgium and meet with British defence officials in London. He began his trip on Sunday in Israel, where he underscored US defence support in meetings with Prime Minister Benjamin Netanyahu and Defence Minister Benny Gantz.

Austin, a former four-star Army general whose overseas military experience was primarily in Iraq, assured German officials of intentions by the Biden administration to keep troops in Germany, though the number is subject to discussion as part of a months-long global review of the basing of US troops. Last year, Trump ordered the number in Germany reduced by about 12,000, to about 24,000.

In his first visit to NATO headquarters in Brussels since taking office, Austin will meet with Secretary-General Jens Stoltenberg, who declared on President Joe Biden's inauguration day that the arrival of a new administration marked the start of a new chapter for the trans-Atlantic alliance.

Trump's departure from the world stage gave the Biden administration an opening to restore a more supportive US approach to Europe and the NATO alliance, but complications will persist. For example, the NATO allies are anxious for Biden to decide whether to pull out of Afghanistan. NATO has more troops there than does the United States, and Biden's indecision troubles them, not least because they count on US military support for removing troops and equipment.

The attack on Iran's Natanz nuclear facility further complicates US efforts to draw Iran back into a nuclear deal. Austin was asked about this earlier Monday while in Israel, and he said only that he expects the administration's diplomatic efforts with Iran will continue.

On the broader horizon, the European allies remain uncertain how their defence and security relationship with the United States will be affected by Biden's push to focus more on China as the chief threat to US security.

That shift in US thinking began during the Obama administration, which announced a pivot to Asia that left Europeans thinking their US ally was turning its back. Washington adjusted diplomatically and rhetorically, assuring the Europeans that it was just a rebalancing.

Then came Trump. His administration further emphasised China as the prime security threat, but of greater concern to the Europeans was his frequent, sometimes shocking, denigration of the trans-Atlantic partnership that had been the foundation of US security policy for decades.

He dismissed the NATO allies as freeloaders, and last summer he ordered the removal of about one-third of the US force in Germany, as well as the move of US European Command headquarters from Germany to Belgium.

“We don't want to be the suckers any more,” Trump told reporters last July, calling the Germans ingrates who don't spend enough on defence but expect the United States to protect them from Russia.

Germany has been an anchor for the US military presence in Europe since the early post-World War II years. Besides hosting the headquarters for US European and US Africa commands, Germany's Ramstein Air Base is headquarters for NATO air and missile defences. The US Army's largest overseas hospital, the Landstuhl Regional Medical Center, is a few miles from Ramstein Air Base. The US Air Force also has a substantial presence in Germany, including the 52nd Fighter Wing at Spangdahlem.

In his first speech to an international audience, Biden in February declared to the Munich Security Conference: America is back, the trans-Atlantic alliance is back, and we are not looking backward. We are looking forward together.

Biden suspended the Trump decision on a partial withdrawal of troops from Germany, which had not yet been implemented. It seems likely the administration will decide not to carry out the Trump order.