They said trade and economic activity had slowed down sharply.
Iraq became more dependent on imports after postwar looting and 13 years of a crippling economic embargo all but wiped out its industrial base.
"Baghdad has been effectively isolated," said Muzahim al-Azzawi, executive manager of Jazairi Transport.
He said truck movement had mostly stopped on the western roads to Jordan and Syria, and that a bridge on the only road left open to Baghdad from the south was now too weak to cross because of war damage and recent sabotage.
The western route leading to Jordan, Syria and Lebanon accounts for an estimated 70% of Iraqi shipments.
"A few trucks try to cross now and then, but the problem is that the resistance stops them on suspicion that they are carrying supplies for Americans," al-Azzawi said.
Iraqi civilian passenger movement has also been disrupted by violence and more people have been opting to fly, taking planes from Baghdad airport that perform sharp evasive manoeuvres to escape possible shoulder fired rocket attacks.
The highway situation forced the oil ministry to stop importing fuel through Syria, Jordan and the Gulf.
Shippers said the only remaining road to Turkey was dangerous and the border was hard to cross.
Highways leading to Jordan and Syria pass through or near Falluja, scene of clashes over the past two weeks between Sunni Muslim fighters and US forces.
The resistance fighters have targeted convoys carrying US supplies.
Resistance has spread west to the Iraqi-Syrian border.
Five US Marines were killed near the border in fighting there on Saturday.
Iraq's imports come mostly from the west and the south, which has experienced an upsurge in Shia resistance after relative postwar calm.
"They would be stolen in no time if we tried. We have no shortage of stock any way. Sales are not as high as they were two weeks ago"
Jasim Abd al-Khaliq,
US forces have also closed the main road leading to the city of Mosul, a trading post with Syria.
Another southern road leading from Baghdad to the port city of Basra was closed after the bridges were blown up.
Road closures and rising crime on the highways and in the cities hurt business.
A salesman at Isam car dealership said the company had imported thousands of cars through the Jordanian port of Aqaba and the Gulf since the war - but none over the past two weeks.
"They would be stolen in no time if we tried. We have no shortage of stock any way. Sales are not as high as they were two weeks ago," Jasim Abd al-Khaliq said.
The showroom was filled with German and Japanese used cars popular in Iraq.
Another business, the Honey Market, which has been doing brisk business selling imported food, said its stocks had started to run out. The Honey Market's shelves, usually filled with Western food and confectionary, were slowly emptying.
"Our suppliers are in Lebanon and Jordan," owner Khalid al-Qas said. "We simply cannot replenish."