Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

LITTLE ROCK / HOUSTON - Arkansas on Tuesday launched an investigation into an Exxon Mobil pipeline rupture that spilled thousands of barrels of crude oil into a housing development last week, just as forecast rain was expected to complicate the clean-up.

Arkansas Attorney General Dustin McDaniel asked Exxon to preserve all documents and information related to Friday's spill and ongoing recovery at the site in Mayflower, Ark., about 20 miles northeast of Little Rock.

"This incident has damaged private property and Arkansas's natural resources. Homeowners have been forced from their homes," McDaniel said in a statement. Asking Exxon to secure the documents is the "first step in determining what happened and preserving evidence for any future litigation," he said.

Exxon spokeswoman Kim Jordan said the company will "cooperate fully" with any investigation.

The spill from Exxon's 848-mile Pegasus line, which covered lawns and snaked down residential streets, forced the evacuation of 22 homes as police blockaded the affected area. On Monday, the strong smell of oil, which resembled asphalt, permeated the town far beyond the affected area.

The incident has received widespread attention and stoked a national debate about the safety of carrying rising volumes of heavy crude from Canada into the United States.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Some environmentalists have used the incident to illustrate why pipelines, such the proposed Keystone XL line that would carry Canadian crude to the U.S. Gulf Coast, should not be built.

Exxon said in a statement on Tuesday that fourteen "oiled" ducks, two turtles, and one muskrat have been recovered for treatment following the spill. Two other ducks were found dead, the oil major said.

The pipeline remained shut on Tuesday, and Exxon had yet to say how long repairs would take and when the pipeline might restart. It was so far unclear how much oil had been spilled, though the company said on Tuesday that 12,000 barrels of water and oil had been recovered.

A plan to allow residents to return to their homes was under way, Exxon said, though the speed of the return would depend on getting the go-ahead from state health authorities.

The company was developing a plan to excavate, remove and replace the ruptured portion of the near 65-year-old line, which transports Canadian crude oil from Illinois to Texas. Excavation is crucial in determining the cause of a pipeline spill.

Meanwhile, rain, which is forecast for Tuesday afternoon and expected to remain on and off for at least two days, may complicate efforts to clean up the spill, which is not far from Lake Conway, a popular fish and wildlife area stocked with bass, catfish, bream and crappie.

Local responders that included firemen, city employees, county road crews and police built dikes of dirt and rock which stopped crude from fouling the lake, said Faulkner County Judge Allen Dodson on Sunday.

Exxon later deployed 3,600 feet of boom near the lake as a precaution.

Exxon spokesman Alan Jeffers said that rain will not hamper clean-up efforts, but there was the potential for rain to carry some of the oil sheen towards the lake.

"Our big focus is to keep it from moving from the ground to the lake," Jeffers said.