Saudi Arabia, Egypt, Bahrain and the United Arab Emirates have cut diplomatic ties with Qatar, accusing it of destabilising the region.
The countries say Qatar is supporting terrorist groups including the Muslim Brotherhood.
The Saudi state news agency SPA said Riyadh had closed its borders, severing land, sea and air contact.
It cited officials as saying it was to "protect its national security from the dangers of terrorism and extremism".
Egypt has also closed its airspace and ports for all Qatari transportation, the foreign ministry said.
The United Arab Emirates has given Qatari diplomats 48 hours to leave the country. Abu Dhabi accuses Doha of "supporting, funding and embracing terrorism, extremism and sectarian organisations," state news agency WAM said.
Bahrain's state news agency said the country was cutting ties with Qatar over "shaking the security and stability of Bahrain and meddling in its affairs".
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A man suspected of planting bombs in New York and New Jersey is in custody after a shootout with police that began when he was found asleep in a doorway.
Afghan-born Ahmad Khan Rahami, 28, is undergoing surgery for a gunshot wound after the confrontation in New Jersey.
Republican Donald Trump immediately seized on the news as vindication of his hard line on immigration and vowed to defeat "radical Islamic terrorism".
The FBI said no other suspect was being sought over the weekend's blasts.
A huge manhunt was sparked on Monday after police publicly identified Mr Rahami as chief suspect.
Officers have refused to discuss what led them to him but senior law enforcement officials have told US media that a fingerprint collected from an unexploded device in New Jersey was key.
The shootout happened in Linden, four miles (6km) south-west of the city of Elizabeth, where further devices were found late on Sunday.
Linden Mayor Derek Armstead said the suspect was found sleeping in the doorway of Merdie's Tavern by the owner, who reported him to police.
When a police officer went to investigate and wake him, the suspect fired on him and two police officers suffered injuries, before his arrest.
Media captionA bomb disposal robot tried to disarm a device in Elizabeth
At a rally in Florida later on Monday, Mr Trump said Mr Rahami would be indulged by US authorities and this was evidence the country had become weak.
"Now we will give him amazing hospitalisation. He will be taken care of by some of the best doctors in the world."
He repeated calls for "extreme vetting" that would include an assessment of whether potential immigrants share American values.
Mr Trump also addressed revelations that the Department of Homeland Security mistakenly granted US citizenship to at least 858 immigrants who came from "special interest countries", which present a security concern or have high rates of immigration fraud.
He warned that Democratic rival Hillary Clinton's "open border" policy would only lead to more incidents such as the attacks in Minnesota and New York.
Mrs Clinton has accused him of enabling terrorists and instead pledged to build trust between law enforcement and Muslim-American communities.
The FBI said they have evidence linking Mr Rahami to devices in both New Jersey and New York, but there was no indication a terror cell was active in the area.
What we know:
Ahmad Kham Rahami has been arrested in connection with the New York and New Jersey blasts
He is a naturalised US citizen born in Afghanistan
What we do not know:
Motivation for the attacks or whether he was radicalised
Whether there is a link to the so-called Islamic State
How exactly authorities pinpointed Mr Rahami as the suspect behind the bombings
Image copyrightAFPImage captionThe suspect was taken into custody on Elizabeth Avenue in Linden, according to reports
The bombing in the Chelsea district on Saturday night injured 29 people. An unexploded device was found nearby.
Other devices have been found or have exploded in New Jersey over the past few days.
Early on Saturday, a pipe bomb exploded in a shore town ahead of a charity race. No-one was hurt.
One of several devices found in an abandoned backpack near the railway station in Elizabeth exploded as a police robot was trying to disarm it in the early hours of Monday morning.
Local residents in Elizabeth, who had encountered Mr Rahami in his work at the family's fried chicken bar, said the family were ordinary and "Americanised".
"He's a very friendly guy, that's what's so scary," said Ryan McCann.
President Barack Obama, speaking in New York, said officials did not believe there was a connection between events in New York and New Jersey and a stabbing attack in Minnesota, also on Saturday, in which nine people were injured.
The president said that the US would continue to go after so-called Islamic State (IS).
"We will continue to lead the global coalition and the fight to destroy Isil [IS] which is instigating a lot of people over the internet to carry out attacks," he said.
