Scott Olson via Getty Images MYRTLE BEACH, SC - JANUARY 16: Republican presidential candidate Sen. Ted Cruz (R-TX) speaks to guests at the 2016 South Carolina Tea Party Coalition Convention on January 16, 2016 in Myrtle Beach, South Carolina.

MYRTLE BEACH, S.C. (Reuters) - The growing feud between Republican front-runner Donald Trump and his central rival Ted Cruz intensified on Saturday with tit-for-tat attacks that put to rest any notion that their debate night fight was a solitary engagement.

The split between the two is evidence of the closeness of the race for the 2016 Republican presidential nomination, particularly in Iowa. Polls there show a neck-and-neck battle with little more than two weeks to go until Iowa on Feb. 1 stages the first nominating contest on the road to the Nov. 8 election.

Trump, who needs a victory in Iowa to set a winning tone to his campaign, kept up his attempt to undermine Cruz's attempt to portray himself as an outsider to the political establishment.

Trump seized on a report in The New York Times that said Cruz had failed to disclose a second loan, from Citibank, that helped bankroll his 2012 Senate campaign. The Times earlier had reported that Cruz had not disclosed a loan from Goldman Sachs for the same campaign.

TIMOTHY A. CLARY via Getty Images Republican presidential candidate Donald Trump speaks at the South Carolina Tea Party Convention at the Springmaid Beach Resort in Myrtle Beach, South Carolina on January 16, 2016.

Cruz's campaign has said the failure to report the loan was a paperwork error.

"He didn't report his bank loans," Trump told delegates to the South Carolina Tea Party Convention.

Some booed Trump for criticizing Cruz since they had cheered Cruz when he spoke to the group earlier.

"Say whatever you want," Trump said in response to the boos. "He didn't report his bank loans... And then he acts like Robin Hood. Say whatever you want.."

Cruz did not mention Trump to the Tea Party event but talking to reporters in Fort Mill, S.C., earlier in the day he was unsparing.

He suggested the New York billionaire and former reality TV star lacks the temperament to be president, pointing to his frequent Twitter assaults on his adversaries. He said Trump had attacked him because Cruz was a threat to him in Iowa.

"I think in terms of a commander-in-chief, we ought to have someone who isn't springing out of bed to tweet in a frantic response to the latest polls," Cruz said. "I think the American people are looking for a commander-in-chief who is stable and steady and a calm hand to keep this country safe."

Trying to prove Trump is not the conservative he says he is, Cruz's campaign released a video entitled "Donald Trump's New York Values" that linked to a 1999 interview Trump did on NBC's "Meet the Press" in which Trump declared he favored a woman's right to abortion and supported gay marriage.

The two candidates had clashed at the last Republican debate, on Thursday in Charleston, over the issue of "New York values" with Trump saying Cruz had insulted the city that absorbed the Sept. 11, 2001, attacks and rebounded.

Trump brought up the issue again at a town hall meeting in Portsmouth, N.H., hours before a scheduled address at the South Carolina Tea Party Convention in Myrtle Beach.

Cruz's criticism of New York, he said, was a "total disgrace."