The US has urged Saudi Arabia and its regional allies to ease their blockade of Qatar, warning it is harming the regional struggle against extremism.
US Secretary of State Rex Tillerson said Qatar must do more to crack down on support for terrorism but that the crisis must not disrupt action against the Islamic State group.
"The blockade is hindering US military actions in the region and the campaign against ISIS," Tillerson said, using the US government's preferred acronym for the group.
Mr Tillerson's comment came as Germany called for greater diplomatic efforts to resolve the Qatar crisis and said Arab states should lift their blockade of the small Gulf state and avoid any escalation into violence.
"Along with our American colleagues but above all our colleagues in the region, we must try to find solutions, especially lifting the sea and air blockades," Germany’s Foreign Minister Sigmar Gabriel said.
"We're talking about food and many other things," he said.
Saudi Arabia, the United Arab Emirates, Egypt and Bahrain cut ties with Qatar this week over its alleged support for terrorism and the agenda of regional arch-rival Iran.
Qatar has dismissed the charges as baseless.
The dispute has created a major diplomatic test for the US, which is a close ally of the countries on both sides.
Washington relies closely on the countries on both sides of the dispute for its military operations in the Gulf.
Qatar hosts the US Air Force's biggest base in the region, while Bahrain hosts the US Navy. Both Saudi Arabia and Qatar have funded rebels fighting in the Syrian civil war.
The confrontation erupted just weeks after US President Donald Trump visited Saudi Arabia. Trump initially responded by tweeting his support for moves against Qatar, even as his State Department and Defense Department sought to remain neutral.
Mr Tillerson, whom Mr Trump has tasked with de-escalating the dispute, said it is "troubling to the United States, the region and to many people who are directly affected."
"We call on Qatar to be responsive to the concerns of its neighbors," he said.
"Qatar has a history of supporting groups that have spanned the spectrum of political expression from activism to violence.
"The emir of Qatar has made progress in halting financial support and expelling terrorists from his country, but he must do more and he must do it more quickly."
Qatari Foreign Minister Sheikh Mohammed bin Abdulrahman al-Thani, speaking after talks in Germany with Mr Gabriel, said the blockade of Qatar broke international law.
He also described the severing of links to his country as "collective punishment".
He said: "These procedures that were taken (are) clear violations of international law and international humanitarian law. They will not have a positive impact on the region but a negative one."
Earlier, the four Arab nations stepped up pressure on Qatar, issuing a list of dozens of people designated as terrorists with alleged links to Qatar.
Sheikh Mohammed said it included journalists and other individuals with no relationship to Qatar. Some had never even visited the country, he said
Many of the others added to the list are figures associated with the Muslim Brotherhood who have made Qatar a base, including Brotherhood spiritual leader Yousef al-Qaradawi. Some are prominent jihadists who have fought in Libya and Syria.
Qatar has angered its neighbours for years by supporting the Brotherhood, a decades-old movement that calls for rule based on Islamic principles.
Turkish President Tayyip Erdogan, whose AK Party has its roots in Islamist politics and who has voiced support for the Brotherhood, signalled his firm backing for Qatar by swiftly signing a law to send Turkish troops to a base there.
Showing how urgently Turkey is treating the matter, parliament passed the law on Wednesday, Erdogan signed it yesterday and it was published in the state gazette today.
Turkey will send warplanes and warships to Qatar after an initial deployment of troops to a Turkish base there, the mass-circulation Hurriyet newspaper said on its website.
Mr Gabriel's spokesman Martin Schaefer later urged Iran, a Shi'ite state that Sunni Saudi Arabia accuses of supporting militant groups across the Middle East, to refrain from any move that could exacerbate the crisis.
"It is important that nothing is done on the other side of the Gulf ... to pour oil on the fire," he said. Germany would try to promote dialogue but did not intend to become a key mediator in the crisis, he added.
Mr Gabriel was optimistic that diplomatic efforts could resolve the crisis and said "it must not end in further escalations that include violence."
Many countries in the region, including Turkey and Saudi Arabia, had previously supported organisations viewed by Germany as dangerous, Mr Gabriel said.
Germany would pursue its concerns about indirect support for militant groups by individuals living in Qatar via its intelligence services, said Gabriel, adding that he believed Doha would respect its agreements with Berlin.
Crisis in the Gulf: Why is Qatar under siege?
The Gulf crisis has sparked fears of military escalation in an already volatile region. However, the Qatari foreign minister downplayed the likelihood of military conflict.
"We don't see a military solution as an option" to the crisis, Sheikh Mohammed bin Abdulrahman Al-Thani said.
Saudi Arabia, the UAE, Egypt and Bahrain have suspended all flights to and from Doha and closed off sea and air links to Qatar.
Saudi Arabia has also sealed off Qatar's only land border, a crucial lifeline for food imports.
The United Arab Emirates central bank also instructed local banks to stop dealing with 59 individuals and 12 entities with alleged links to Qatar and to freeze all their assets, the state news agency WAM reported today.
Armed Qatari gunboats patrolled the corniche of the capital Doha this morning. A picture on Facebook showed a supermarket displaying food from Turkey including milk, eggs and chicken.
Qatar - the world's largest exporter of liquefied natural gas - has vowed to ride out the isolation imposed on it by fellow Arab states and said it would not compromise its sovereignty over foreign policy to resolve the region's biggest diplomatic crisis in years.
Sheikh Mohammed said the country could survive "forever", adding that it respected international agreements and would continue supplying liquefied natural gas to the UAE.
Qatar is home to 2.7 million people but only about 300,000 citizens. Most of its population comprise foreign workers that helped to build the tiny finger off the Arabian Peninsula into a natural gas exporting powerhouse, crowned with skyscrapers. Other projects include soccer stadiums for the 2022 World Cup.
In an apparent escalation of the crisis, staff at Al Jazeera, Qatar's influential satellite television news channel which often infuriates the rulers of the Arab world, said its computer systems had come under cyber attack.
