A Pennsylvania pastor accused of sexually assaulting and impregnating a teenager has been sentenced to between three to six years after pleading guilty.

Jacob Malone, a 35-year-old from Exton, must also register as a sex offender for 15 years.

Malone pleaded guilty to institutional sexual assault, corruption of minors and child endangerment, WTXF reported. Judge Jacqueline Cody rejected an earlier plea agreement that called for a two-year minimum jail term.

Malone worked for a non-denominational church called Calvary Fellowship in Downingtown in 2014 when authorities said he began sexually assaulting the girl. The victim, who was 18 years old when the abuse began, was made pregnant by him and gave birth to their daughter a year ago.

Philly.com reported that she told authorities that Malone raped her several times while she lived with him, his wife and their children in West Whiteland Township. She said Malone took advantage of her "mentally, physically, spiritually".

Malone admitted in court to giving the girl alcohol but maintained that the sexual encounters between them were consensual. He apologised and said his "failures and weaknesses" had hurt her, her family and his family.

"She admired me and trusted me, and I betrayed that," he said. According to AP, the original charges against Malone included rape.

Evan Kelly, defending, said that Malone had been adamant that he did not commit rape. He was accused of victimising her over several years in a number of states.

He left the US after a warrant for his arrest was issued but was arrested at Newark Liberty International Airport in January 2016 after returning from Ecuador.

Cody said the case was "one of the times when the court system fails" and lamented that Malone would be "serving a sentence much lighter than the crime deserves". Malone will get credit for the more than one year he has already served since his arrest.

The victim "is pleased he will be spending an additional year in jail," District Attorney Emily Provencher said.