WASHINGTON - Republican front-runner Donald Trump on Tuesday abandoned a pledge to support a party presidential nominee other than himself, a sign of increasing friction with chief rival Ted Cruz.

"No, I don't anymore," Trump replied, when asked at a CNN town hall event whether he still supported a pledge he made last year to support whoever is the Republican nominee for the Nov. 8 election.

Trump's signing of a loyalty pledge last September was important in helping him gain credibility within the Republican National Committee. The pledge was also signed by all his rivals for the presidential nomination.

His aboutface came as he tries to fend off a challenge from Cruz, a U.S. senator from Texas who is running second to the New York billionaire in the race for the 1,237 delegates needed to win the nomination.

Trump and Cruz were enmeshed in a fight last week involving their wives, with a Cruz SuperPAC publishing a provocative photo of Trump's former model wife, Melania, and Trump retaliating by tweeting an unflattering photo of Cruz's wife, Heidi.

Cruz, asked earlier at the CNN town hall whether he also would honor the pledge to support the nominee if it was not himself, declined to give a straight answer.

"Let me tell you my solution to that," Cruz said. "Donald is not going to be the GOP nominee. We're going to beat him."

GOP is the acronym for Grand Old Party, a nickname for the Republican Party.

Trump said he could do without Cruz's support.

"I watched him tonight and I watched how tormented he was when you asked him that question," Trump told CNN moderator Anderson Cooper. "I don't want to have him be tormented. Let me just tell you I don't want his support, I don't need his support. I don't want him to be uncomfortable."

Trump also said he recognized that several of those who have dropped out of the race might harbor ill feelings towards him, mentioning former Florida Governor Jeb Bush, Wisconsin Governor Scott Walker and U.S. Senator Rand Paul of Kentucky.

Walker endorsed Cruz earlier on Tuesday, with Wisconsin's primary vote coming up on April 5.

"I drove him out of the race," Trump said of Walker, who abandoned his presidential bid last autumn. "I drove Jeb Bush out of the race, I drove Rand Paul out of the race. I understand why they don't like me."

A third Republican presidential candidate, Ohio Governor John Kasich, was also tentative about honoring the pledge. He told the town hall he had been "disturbed by some of the things I've seen" during the campaign, adding, "I want to see how this finishes out."