STORY: RUTTE: "If NATO can help, obviously NATO is there."

NATO Secretary General Mark Rutte on Thursday said that some alliance members were initially "a bit slow" to provide assistance to the U.S. in Iran...

RUTTE: "...In fairness, they were also a bit surprised."

But he added there is now a "massive amount" of support, including basing and logistics.

The comments come a day after his White House meeting with U.S. President Donald Trump, who has criticized European allies in recent weeks for what he said was inadequate support.

Diplomats who spoke to Reuters said Rutte told European governments that Trump wants concrete commitments within days to help secure the Strait of Hormuz.

Rutte is also working to defuse a crisis after Trump said he was considering withdrawing from the 32-member transatlantic alliance.

On Thursday, a senior White House official told Reuters that Trump has discussed with advisers the option of removing some U.S. troops from Europe.

The official, who requested anonymity to discuss internal deliberations, said no decision has been made, and the White House has not directed the Pentagon to draw up concrete plans for a troop reduction on the continent.

European leaders are now under pressure to show they are quickly making tangible plans to help secure the Strait of Hormuz.

RUTTE: "This alliance is not whistling past the graveyard, as you would say in the United States. Allies recognize, and I recognize, we are in a period of profound change in the transatlantic alliance. Europe is assuming a greater and fairer share of the task of providing for its conventional defense."

Multiple European allies have said they're willing to help in the Strait of Hormuz, but only once the situation is less hostile, and an agreement with Iran is made that their ships will not be attacked.