WASHINGTON - Republican presidential candidate Donald Trump called US President Barack Obama and Democratic candidate Hillary Clinton "co-founders" of Islamic State on Thursday, igniting fresh criticism of his inflammatory campaign style.

The New York real estate developer has previously attacked Obama and Clinton, secretary of state from 2009-13, for how the United States pulled out of Iraq after the war, saying it helped create the militant Islamist group that has seized swaths of Iraq and Syria.

The idea that a sitting US president created a militant group determined to kill Americans and other Westerners took that line of attack to a new level. Trump first made the assertion in a speech Wednesday night in Florida. He repeated it in an interview Thursday morning with CNBC.

His remarks followed a troubled week for the Republican candidate. Party leaders urged Trump to focus on the campaign to beat Clinton after he drew strong criticism for a persistent confrontation with the family of Muslim American soldier who died in Iraq and for his initial refusal to support prominent Republican congressional candidates in their primary races.

Recent opinion polls have shown Trump losing ground to Clinton, a former US senator and first lady, in the race for the Nov. 8 election. An average of polls by RealClearPolitics has Clinton 7.7 percentage points ahead, at 48 percent to his 40.3 percent.

"He (Obama) was the founder of ISIS. And so was she. I mean I call them co-founders," said Trump, who says he opposed the Iraq war. "He shouldn't have gotten out way he got out. It was a disaster, what he did," he told CNBC. US House Democratic Leader Nancy Pelosi on Thursday said the recent cyber attack on Democratic politicians was "broad" and that Russians were clearly behind the breach, adding that the damage was still being investigated. "It is the Russians," Pelosi told reporters at a news conference, referring to the recent breach affecting the Democratic Congressional Campaign Committee.  Pelosi called the attack, made public last month, an "electronic Watergate" akin to the 1972 burglary at Democratic Party headquarters at the Watergate office that upended the Nixon presidency. "This is a break-in."

Meanwhile, a man spent three hours Wednesday scaling Trump Tower, the New York home and headquarters of the Republican nominee for US president, before police captured him through an open window.

Live television footage showed uniformed New York police officers reaching out and grabbing the young man with curly auburn hair - dressed in grey shorts, an olive T-shirt and white cap - some three hours after he started his ascent using five suction cups.

The 20-year-old Virginia man wanted to meet Trump, police said, without providing his name. He had been edging his way up the side of the building gingerly - sometimes with his feet dangling precariously as he gripped the suction cups - on a hot and steamy afternoon.

New York billionaire Donald Trump was outside the city on Wednesday, holding a rally in Virginia with another event planned later in Florida.

Police who received an emergency call around 3:30 pm (1930 GMT) initially believed they were dealing with someone who wanted to jump from the building.

"We were able to break a window and establish some type of dialogue and we then secured three jumper air bags and numerous amounts of equipment for a high-angle rescue job," Manhattan South police commander William Morris told reporters after the incident.

A crowd of mesmerized onlookers watched the climber along with reporters and police, who cordoned off the block between Fifth and Madison Avenues.

The climber wanted a face-to-face meeting with Trump, as explained in an anonymous YouTube video, Morris said.

"At no time did he express that he wanted to hurt anybody," he added. "His sole intention was to meet with Mr Trump."

In the video, titled "Message to Mr Trump (why I climbed your tower)," a young man dressed in a black hoodie with his face partially obscured exhorted Americans to vote for the Republican in November.

"The reason I climbed your tower was to get your attention," the man said, addressing the White House candidate and identifying himself as "an independent researcher."

"As for anyone else who's watching, please help make this video go viral so that it gets to Mr Trump and be sure to get out and vote for Mr Trump in the 2016 election," he added.

There was no immediate confirmation about the video's authenticity.

Police removed two windows from the 21st floor and it was there that officers grabbed him around 6:35 pm (2235 GMT).

The climber had started his ascent from a terrace area on the fifth floor and managed to initially evade police by climbing around an opened window and washer scaffold.

Police took him to a hospital for a psychological evaluation, after which he would be arrested, Morris said.

"We're working with the Manhattan District Attorney's office to determine the appropriate charges," he said.

Trump lives in a marble triplex at the top of the 68-story building, which is also the headquarters of his Trump Organization and election campaign.

The Republican nominee unleashed a firestorm on Tuesday when he suggested that "Second Amendment people" - those who support gun rights - could take action to stop Hillary Clinton from appointing US Supreme Court justices as president.

Since he launched his controversial, media-saturated bid for the White House, the tower on New York's prestigious Fifth Avenue has become a magnet for tourists.

Members of the public are free to roam inside the atrium until 10 pm most days as part of an agreement that allowed Trump to build 20 stories higher.