Jordanian security forces have seized 350,000 pills hidden in desert areas, a police spokesman said on Tuesday.
It was the latest announcement of a narcotics bust in the kingdom, which is engaged in a drugs war on its borders with Syria.
Spokesman Amer Al Sartawi said anti-narcotics personnel received a tip-off that the pills were stored in a remote area near Ruwaished, an eastern town on the Amman-Baghdad road, about 50km south of the border with Syria.
A search team found the pills in three large bags hidden among rocks.
"Investigations have started to apprehend the ring leader in the case, and his accomplices," said Mr Al Sartawi, without giving further details.
Ruwaished is inhabited by tribes who have traditionally formed the bedrock of the political system in Jordan.
Arab officials say that in the past five years the area has turned into a supply route for narcotics from areas under the control of the Syrian government in the south of the country to Jordan, and then to Saudi Arabia.
Jordan, which is also a market for the drugs, has accused the Syrian military and pro-Iranian militias allied with it of sponsoring the narcotics smuggling, particularly the amphetamine pills known as Captagon.
A Captagon pill is cheap to produce and can be sold for up to $20.
Syrian President Bashar Al Assad has denied that the authorities in the country have anything to do with the drugs. He blamed countries he did not name for the trade, as part of what he calls a deliberate creation of chaos in Syria.
In May, Mr Al Assad was invited to an Arab League summit, which was held in Riyadh, for the first time since the Syrian civil war started in late 2011, after security forces violently suppressed a protest movement against Mr Al Assad's 23-year rule.
Jordan has a 360-kilometre border with Syria that has been partly fenced. The US, and other western donors, have also spent hundreds of millions of dollars in the past several years helping the Jordanian military install surveillance and monitoring systems on the border.
The kingdom has supported the Arab rapprochement with Damascus, and indicated that Mr Al Assad must reciprocate by co-operating on the drug issue.
However, Jordan has continued to announce infiltration attempts from within Syria, the latest of which was at the start on this month, when the military said it intercepted a drone carrying crystal meth, a synthetic drug, from Syria.
