Defense Secretary Mark Esper said Thursday that the U.S. military has completed President Trump’s order to withdraw troops from northeastern Syria.

Esper told Reuters that about 600 U.S. troops now remain in Syria, representing a 40 percent drop in troop levels in the country. The Pentagon chief emphasized in an interview that he retained the authority to move a small number of troops in and out of Syria, adding that the number of troops would hover around 600 for the foreseeable future. 

“It will be relatively static around that number. But if we see things happen … I can dial up a little bit,” he said. 

He also said that U.S. troop levels in Syria could continue to drop if European allies deployed more forces to the country. He did not, however, suggest that a new contribution to the U.S. mission in Syria was in the making. 

“The coalition is talking a lot again. We could see some allies want to volunteer troops,” Esper said. “If an allied country, a NATO country, decided to give us 50 people, I might be able to turn off 50 people.”

Trump in October abruptly announced that the Pentagon would pull hundreds of U.S. troops from northern Syria ahead of a planned Turkish incursion in the region. Esper said later that month that troops leaving Syria would be relocated to western Iraq, where they would continue to conduct operations to prevent a resurgence of ISIS.

Trump’s decision to remove forces from northern Syria was met with bipartisan backlash, with many arguing that the move amounted to a betrayal of the Kurdish YPG, which leads the Syrian Democratic Forces. 

The Kurdish-led forces proved to be the U.S.’s most effective allies in the fight against ISIS. Turkey has long considered the Kurdish YPG to be a terrorist insurgency. 

Trump on Wednesday held a meeting with Turkish President Recep Tayyip Erdoğan on the sidelines of a NATO summit in London. The president told reporters that the two had a “good meeting” focused on the situation at the Syrian border. 

“We discussed Syria, we discussed the Kurds, we discussed numerous things and we’re getting along very well,” he said.