WASHINGTON — Iran appears to have stopped shipping the deadliest type of weapons used against U.S. troops in Iraq after a European government confronted Tehran with proof that the weapons came from Iranian factories and Iraqi officials warned their neighbor that instability in Iraq affects the entire region, U.S., Western and Iraqi officials said.

A senior U.S. general in Iraq said Thursday that Iran is upholding informal commitments it's made in the last several months and no new weapons caches have been found recently. "We believe the commitments that the Iranians have made appear to be holding up," said Maj. Gen. James Simmons, a deputy corps commander in charge of studying explosive attacks, during a press briefing.

That's a striking departure from repeated U.S. condemnations of Iranian meddling in Iraq and from the argument by allies of Vice President Dick Cheney that there's little point in negotiating with Iran because its leaders can't be trusted to deal in good faith.

A Western diplomat with knowledge of the incident and two U.S. intelligence officials told McClatchy that the Iranians began curbing their support for anti-American forces in Iraq and Afghanistan after they were caught supplying explosively formed penetrators, or EFPs, to the Taliban in Afghanistan. Similar weapons have turned up in southern Iraq, the Western diplomat said.

EFPs are sophisticated bombs that have caused extensive U.S. casualties in Iraq by firing molten copper plugs through the armor of U.S. tanks and Humvees.

A European government delivered a demarche, a diplomatic protest, to Tehran several weeks ago after truckloads of Iranian weapons were intercepted entering Afghanistan on at least four occasions, the Western diplomat and the U.S. intelligence officials said.

When Iranian officials denied any involvement, European diplomats showed them photographs of markings on the weapons that identified the Iranian factories where they were produced, they said. The photographs "had a major impact," said the Western diplomat.

The Western diplomat and the U.S. intelligence officials requested anonymity because they weren't authorized to speak publicly. For the same reason, they declined to identify the European government that delivered the protest.

At their peak in July, there were 99 EFP attacks in Iraq, according to Lt. Gen. Raymond Odierno, the No. 2 U.S. commander there. Last month, there were 30.

The officials, who requested anonymity because of the sensitivity of the issue, cautioned that it's too early to conclude that the weapons flow has been turned off. Iran, they said, could quickly reopen the tap.

"Let's see if we're looking at a trend or an aberration," said one U.S. official.

U.S. officials in Iraq also said that despite the reduced arms flow, U.S. troops are still finding large EFP caches in Iraq, but that they're unsure whether those weapons are new or were smuggled in prior to the negotiations with Iran and the discovery of the similar weapons in Afghanistan.

Iraqi, U.S. and European officials said the drop in the arms flow also followed an August declaration of a cease-fire by anti-American Shiite Muslim cleric Muqtada al Sadr, whose Mahdi Army militia was threatening Iraqi Prime Minister Nouri al Maliki's shaky coalition government, which Iran considers an ally.

"The reining in of the Mahdi Army was very helpful," said Iraqi Foreign Minister Hoshyar Zebari, who participated in the talks among Iraq, Iran and the United States.

A senior U.S. official in Baghdad said that Maliki was armed for his talks with Iran with intelligence documenting Iran's involvement.

During meetings in August in Tehran, "we heard from them (Iranians) a strong commitment to cooperate with the Iraqi government," said Sadiq al Rakabi, a Maliki adviser. "Any interference is not acceptable. The prime minister told them that we are looking for real cooperation, that we should turn a new page . . . that instability in Iraq will not only affect Iraq, it will affect the whole region."

Other factors also may have contributed to the decline in Iranian aid to anti-American groups in Iraq and Afghanistan, the officials said. Iran, already under the pressure of international economic sanctions over its nuclear program, may be trying to undercut U.S. calls for tougher sanctions by responding to European and Iraqi demands, they said. The reduced arms flow also has coincided with progress that U.S. and British troops have made recently in suppressing violence in southern and central Iraq.

(Landay reported from Washington; Youssef reported from Baghdad.)