HOUSTON -- The protest movement against the proposed Keystone XL pipeline took its message to the streets of this city yesterday, raiding corporate offices and staging an elaborate street protest that culminated with a rally at a large urban park.

Yesterday about 50 members of the Tar Sands Blockade movement stormed the Houston offices of TransCanada Corp.'s Keystone XL project. The southernmost segment of Keystone XL is currently under construction between Cushing, Okla., and Gulf of Mexico coastal refining facilities.

The group had hoped to occupy the lobby of the office building but was forced out by police after about 30 minutes. But the protest continued in the streets, with activists conducting a street theater in which "a 'pipe dragon' puppet destroyed homes and poisoned water until being slain by knights" representing the coalition opposed to the Keystone XL project, the group said in a statement.

Officials on both sides said the protest action ended without violence or damage to property. Protester organizers said two of their members were arrested.

"Police responded swiftly, and almost all of the protesters peaceably went to the public sidewalk to continue their protest," TransCanada spokesman David Dodson confirmed.

From there the group moved to Memorial Park, where it joined about 50 other protesters for a rally that continued into the afternoon.

Tar Sands Blockade spokeswoman Kim Huynh said yesterday's action was organized over the weekend at a training camp held for activists looking to help with the expanding movement against the Keystone XL project and Canadian oil sands development in general.

"They were very quick to get on the scene and there was a lot of police present, but we did feel like we had made our point and continued with the very low-risk-level activities," she said.

Despite several arrests, cold weather and TransCanada contractors bypassing activists camped out in trees along the company's legal easement secured to build the pipeline project, the protest group says it has no intention of letting up.

Protest activity that began last summer in the far northeastern part of Texas has now spread all the way to Houston. Tar Sands Blockade says it is now teaming with other environmental organizations and even the Internet hacking movement that calls itself Anonymous, and hopes the number of participants engaged in fighting the pipeline project will grow as the warmer summer months approach.

Yesterday's protest was the symbolic start of "a new phase of our campaign, one that's going to be ... very focused on the financial and corporate entities backing Keystone XL," Huynh said.

The giant refining company Valero has also become a target of protesters for its support of the Keystone XL construction and for alleged impacts from refinery pollution in southeast Houston.

The Tar Sands Blockade movement is also working closely with major national environmental nonprofits to organize another anti-Keystone XL rally in Washington, D.C., aimed at pressuring the Obama administration to reject TransCanada's new request that it be allowed to build the Keystone XL line across the Canada-U.S. border.

State governments have the primary responsibility for regulating pipeline construction, but TransCanada needs the federal government's approval to cross the border. The Army Corps of Engineers swiftly reviewed and approved the southern Keystone XL leg construction now under way after an executive order.