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BUDAPEST, Hungary — Austria stepped up vehicle inspections Monday at its Hungarian border after 71 refugees apparently suffocated in a truck, creating a huge traffic jam on the main Budapest-Vienna highway.

In addition to the gridlock at the Hegyeshalom border crossing — about an 18 1/2-mile backup at its peak — traffic was slower than usual at other spots along the Hungary-Austria border, the traffic monitoring firm Utinform reported.

Traffic appeared to be flowing fairly smoothly by late afternoon and Austrian Interior Ministry spokesman Karl-Heinz Grundboeck said they would continue to conduct "spot checks" of vehicles at all main border crossings.

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In Vienna, senior police official Konrad Kogler told reporters that since Austria began the increased checks Sunday they have resulted in the arrests of five human traffickers and the interception of 200 migrants.

Vans and trucks wait for a check control by Austrian border officials on M1 highway in front of the former border station of Hegyeshalom, on August 31, 2015. ATTILA KISBENEDEK / AFP - Getty Images

Austria's increased controls "prove that no European country is going to allow illegal migrants, including refugees, to reach its territory without control," the Hungarian government said.

Hungary is building a 4-meter (13-foot) high fence on its southern border with Serbia to try to stem the flow of migrants and refugees coming across the Balkans. Hungarian lawmakers this week plan to discuss proposals allowing the government to deploy troops to the border and measures increasing penalties for illegal migrants and human traffickers.

About 160,000 migrants and refugees have been detained already this year in Hungary, more than triple the figure recorded in all of 2014. Many apply for asylum but quickly leave the financially-strapped European Union nation for richer EU countries like Germany and Austria before their requests are decided.

Related: Pope Francis: Crimes Against Refugees 'Offend the Entire Human Family'

Austrian police say the 71 refugees likely suffocated in a truck with Hungarian license plates that was abandoned last week in Austria on the Budapest-Vienna highway. Five suspected traffickers have been detained in the case and Hungary is stepping up its arrests of smugglers.

Helmut Marban, an Austrian police spokesman in Burgenland province where the truck was discovered, said another 12 Syrian travel documents had been found on the truck with Hungarian license plates, along with 10 cellphones. Forty autopsies had been carried out so far and results were to be tentatively announced Friday.