Turkey’s prime minister, Recep Tayyip Erdogan, charged on Thursday that the Syrian President Bashar Al-Assad’s government has used chemical weapons against its people.

Speaking to NBC News, Erdogan called on the U.S. to take stronger action in Syria.

“It is clear the regime has used chemical weapons and missiles,” Erdogan said, though he gave no specifics about when and where the weapons were allegedly used.

He indicated, however, that he believes President Obama’s “red line” for the U.S. in deciding whether to take action has been crossed.

“It has been passed long time ago,” said Erdogan, who will meet with President Barack Obama on May 16.

“We want the United States to assume more responsibilities and take further steps. And what sort of steps they will take, we are going to talk about this,” he added.

Erdogan cited as evidence the “remainders of missiles” — at least 200 by his count — that he believes were used in chemical attacks, along with the injuries of Syrians brought over the Turkish border for medical treatment.

“There are patients who are brought to our hospitals who were wounded by these chemical weapons,” he told NBC News.

Erdogan rejected any suggestion that the rebels might have used chemical weapons.

“There is no way I can believe in this now. First of all, how are they going to obtain this? And who will give this to them?” he said.

“But if it exists, we are against this…We are against whoever holds the weapons,” he emphasized.

The White House notified lawmakers late last month that the United States had established, with “varying degrees of confidence,” that a sarin gas attack had taken place in Syria, leading to increased pressure on Obama to act in Syria, after he previously warned that using chemical weapons would cross “a red line”.

The White House has said it is considering all its options, including reviewing its opposition to date to providing weapons to rebels.

Washington said this week, as Erdogan indicated as well, that it was “highly skeptical” of an assertion that Syrian rebels had used chemical weapons, after a UN human rights investigator suggested it was the opposition who had deployed sarin gas.

Erdogan told NBC News he could not confirm that sarin was used in Syria. “We don’t have such a finding yet,” he said.

Asked whether Turkey would support a U.S.-enforced no-fly zone in Syria, Erdogan said, “Right from the beginning…we would say ‘yes.'”

He denied that Turkey has provided military support to the rebels but said his country has spent nearly $1 billion on aid to 300,000 refugees from Syria.

“We keep the open door policy because they are fleeing oppression.” Erdogan told NBC News.

He added that he has heard reports that Assad’s wife and children have already left Syria, their lives “ruined” by him.

“The thing he should do now is to leave Syria,” he said. “Sooner or later, the opposition are going to get him.”