WASHINGTON (Reuters) — U.S. President Barack Obama said on Monday progress needs to speed up against Islamic State militants, calling on allies to increase their military contributions to coalition efforts to destroy the group in Iraq and Syria.

Speaking to reporters at the Pentagon, Obama said he was sending Defense Secretary Ash Carter to the Middle East to secure more military help from partner nations in the fight against the group.

“This continues to be a difficult fight,” Obama said. “We recognize that progress needs to keep coming faster.”

The president ticked off a list of accomplishments by the United States and its allies against the group: Islamic State had lost significant swaths of territory it once controlled in Iraq and Syria, and leaders were being targeted one by one.

“ISIL leaders cannot hide and our next message to them is simple: ‘you are next,'” he said, using an acronym for the group.

The coalition was also targeting Islamic State’s oil tanker trucks, wells and refineries.

“We are hitting ISIL harder than ever,” he said.

Obama, a Democrat, has come under criticism by Republicans for not doing enough to counter Islamic State, in particular since the Nov. 13 attacks in Paris that killed 130 people and were claimed by Islamic State, and the Dec. 2 shooting in San Bernardino, California. Authorities believe the couple who killed 14 people in that attack were inspired by Islamist militants.

The White House has sought to counter those critics by outlining progress made since Islamic State’s rapid rise in Iraq and Syria more than a year ago.

(Reporting by Roberta Rampton and Jeff Mason; Editing by Doina Chiacu and Frances Kerry)

Photo: U.S. President Barack Obama arrives to deliver a statement after attending a National Security Council meeting on the counter-Islamic State campaign at the Pentagon in Washington, December 14, 2015. REUTERS/Carlos Barria