A Texas judge temporarily blocked construction on a small portion of the controversial Keystone pipeline after a landowner sought relief, but operator TransCanada said Tuesday it will have no impact.

Landowner Michael Bishop sought an injunction out of concern that the Canadian tar sand oil that will eventually be transported by the pipeline is more hazardous than typical crude oil and would be harder to clean up in case of a spill.

His concern is echoed by environmentalists, who also oppose the project because exploiting the tar sands requires energy that generates a large volume of greenhouse gases.

TransCanada dismissed Bishop's concern and noted that previous court rulings have determined that the tar sand oil fits within the state's definition of crude oil.

The company hopes to resolve the issue at a hearing on Thursday, spokesman Shawn Howard said.

"Mr Bishop's request does not impact overall construction, and we are on track to bring this pipeline into operation in late 2013," Howard said in a statement.

While some "ground clearing activities" have already taken place on Bishop's property, construction had not yet begun, he added.

Bishop, whose property is in rural Nacogdoches County, about 140 miles (225 kilometers) north of Houston, had previously opposed the pipeline, the Houston Chronicle reported.

But TransCanada said it had reached an easement agreement with Bishop three weeks ago that included a "significant compensation package" and allowed the firm to use his property for the pipeline.

President Barack Obama denied approval for the $7 billion pipeline earlier this year and the US State Department asked for a new route to avoid environmentally sensitive areas.

TransCanada began work in August on a 485-mile pipeline between Oklahoma and the Texas coast that does not require US presidential approval.

The US State Department is currently reviewing the company's revised application for a permit to proceed with the 1,179-mile Keystone XL pipeline from Hardisty, Alberta to Steele City, Nebraska and is expected to announce a decision early next year.

Canada is already the largest energy exporter to the United States. The Keystone XL pipeline would bring 830,000 barrels of oil per day to the Gulf Coast.

"I'd be asking hard questions if they tried to run that gunk through my back yard too," said Anthony Swift, an attorney working on petroleum issues at the Natural Resources Defense Council.

Bishop may have a solid case, he added, noting that the oil industry had previously claimed that the tar sand oil -- or bitumen -- was different from crude in order to get preferential tax treatment.

Both the Internal Revenue Service and Congress have also previously determined that tar sands oil isn't crude.

"Diluted bitumen does not behave like what we normally think of as oil: it is mined or steamed out of the ground, is the consistency of peanut butter and won't even move through a pipeline without a lot of pressure and chemicals to thin it out," said Swift.