A small group of climate activists on Tuesday forced the shutdown of five major pipelines carrying crude from Canada to the United States, stepping up opposition to Alberta's oil industry as it seeks support for major export projects.

United States-based Climate Direct Action said its members worked in groups of two or three at pipeline sites in Washington, Montana, North Dakota and Minnesota on Tuesday morning. The recently formed group posted photos and video that purportedly show how the activists – who said they had researched how to safely shut down the pipelines – cut through security chains, closed valves and were eventually stopped by police at sites belonging to Enbridge Inc., TransCanada Corp., Kinder Morgan Inc. and Spectra Energy Corp.

Climate Direct Action said it closed down the pipelines in solidarity with anti-pipeline protests led by North and South Dakota's Standing Rock Sioux Reservation, but also took the "personal, direct action" to push the U.S. government to enact stricter measures on climate change. The group is calling for a total ban on new fossil fuel extraction and an immediate end to oil sands and coal use.

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The moves mark a further escalation in the battle against Alberta's oil sands industry as it seeks wider access to global markets. Major energy companies have clamoured for years to boost exports of bitumen, but those efforts have been stymied by opponents who claim new pipelines would facilitate added production and accelerate emissions of climate-altering greenhouse gases. Now, even existing infrastructure is in the crosshairs of activist opposition.

"Forget building any new infrastructure, but we need to stop the existing infrastructure that is transporting and extracting," Climate Direct Action spokeswoman Afrin Sopariwala said in a phone interview from Seattle. She said nine activists from the group were arrested.

Calgary-based Enbridge said both its Line 4 and Line 67 pipelines were shut down following "tampering incidents" at facilities in Minnesota. The conduits form part of Enbridge's massive mainline network from Edmonton to Superior, Wisc., that handles the bulk of Canadian crude oil exports to the United States.

A spokesman for the company said Tuesday that it was too soon to say when it would restart operations, but that no impact to shipper deliveries was anticipated.

"The actions taken to unlawfully trespass on our facility in Minnesota and attempt to tamper with energy infrastructure were reckless and dangerous. The groups involved in this morning's activities claim to be protecting the environment, but they do the opposite and put the safety of people at risk – including themselves, first responders and neighbouring communities and landowners," the company said in a statement.

"We take this very seriously and will support the prosecution of all those involved.

TransCanada spokesman Mark Cooper said the company shut down its Keystone pipeline Tuesday as a precaution after activists broke onto property in North Dakota and attempted to disrupt operations. The pipeline resumed deliveries late Tuesday, he said. The 4,200-kilometre pipeline transports Alberta crude to refineries in the U.S. Midwest. It has capacity of 550,000 barrels a day.

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"We notified local law enforcement who will determine arrests, charges of trespass and other criminal offences," he said in an e-mail. "TransCanada supports prosecution to the full extent of the law."

A spokeswoman for Kinder Morgan said activists broke into an unspecified location on the company's Puget Sound pipeline system in Washington state early Tuesday morning. The line connects with the company's Edmonton-to-Burnaby Trans Mountain pipeline at Abbotsford, B.C., with capacity of about 180,000 barrels a day.

The company was not operating that portion of its network at the time and there was no release of product, Ali Hounsell said in an e-mail. Three individuals were arrested by local authorities, she said.

Spectra Energy Corp. said it had restarted its Express pipeline system after activists broke into a locked facility and tampered with a valve Tuesday morning in Montana, forcing a temporary shutdown. The 1,200-kilometre pipeline transports up to 280,000 barrels of oil a day from Hardisty, Alta., as far as Wood River, Ill.

This is not the first time pipelines have been targeted. Enbridge in January was forced to temporarily shut its Line 9 from Sarnia, Ont., to Montreal after it detected a valve had been tampered with and closed on the system. It marked the fourth time in two months its facilities had been targeted. Line 9 gives Eastern Canadian refineries access to crude from Alberta oil fields and the U.S. shale patch. It began operations last year after contentious hearings.

Ms. Sopariwala said her group was inspired by past pipeline shutdowns and took Tuesday's action in solidarity with the Standing Rock Sioux Reservation, where members concerned about water safety and cultural grounds are protesting construction of the $3.7-billion (U.S.) Dakota Access pipeline.