The United Arab Emirates (UAE) threatened to impose an economic embargo against Qatar while Bahrain said "any options" were on the table as the crisis in the Gulf showed no signs of abating on Thursday.
The tough talk from the Gulf Cooperation Council members came on Wednesday despite efforts by US President Donald Trump and Kuwait's emir to prevent a further escalation of the dispute, which started on Monday when Saudi Arabia, UAE and Bahrain, along with Egypt, announced they were severing diplomatic relations with fellow GCC country Qatar.
UAE Foreign Affairs Minister Anwar Gargash told Reuters news agency there would be more economic curbs on Qatar if necessary, and said Doha needed to make ironclad commitments to change what he claimed was a policy of funding armed groups.
Qatari officials have repeatedly denied the allegations.
Gargash later told France 24 television any further steps could take the form of "a sort of embargo on Qatar".
Kuwait's ruler, Sheikh Sabah Al Ahmad Al Sabah, travelled from the UAE to Qatar on Wednesday after visiting Saudi Arabia the day before to resolve the crisis.
But in some of the strongest comments yet, Bahrain's foreign minister, Sheikh Khalid bin Ahmed Al Khalifa, reportedly told the Saudi newspaper Mecca he doubted whether Qatar would change its behaviour.
"We will not hesitate to protect our interests and the road is open to any options to protect ourselves from Qatar," Sheikh Khalid was quoted as saying.
Bahrain, Saudi Arabia, Egypt, the UAE and several other countries cut their ties with Doha on Monday, accusing it of supporting armed groups and their regional rival, Iran - charges Qatar says are baseless.
Gargash said measures taken against Qatar this week were not aimed at seeking new leadership in Doha.
"This is not about regime change - this is about change of policy, change of approach," Gargash told AFP news agency in Dubai.
After apparently showing support for the moves against Qatar in tweets sent on Tuesday, Trump on Wednesday called Qatar's Emir Sheikh Tamim bin Hamad Al Thani and later UAE's Crown Prince Mohamed bin Zayed Al Nahyan to calm the situation.
Trump even suggested a White House meeting among Gulf officials to resolve the crisis.
"First, and most importantly, the leaders agreed on the importance of implementing agreements reached in Riyadh to counter extremism and to combat the funding of terrorist groups," a White House statement said on the talks between Trump and Al Nahyan.
"Additionally, the president emphasised the importance of maintaining a united Gulf Cooperation Council to promote regional stability, but never at the expense of eliminating funding for radical extremism or defeating terrorism," it added.
Saudi Foreign Minister Adel al-Jubeir said Gulf states could resolve the row with Qatar among themselves without outside help.
"We have not asked for mediation, we believe this issue can be dealt with among the states of the Gulf Cooperation Council," he told a news conference in Berlin.
Jubeir declined to confirm a list of 10 demands published by Al Jazeera, which included shutting down the Doha-based news channel but added that Qatar knew what it needed to do to restore normal relations.
In a sign of economic damage from the dispute, Standard & Poor's downgraded Qatar's debt on Wednesday as the country's riyal currency fell to an 11-year low amid signs that portfolio investment funds were flowing out because of the rift.
S&P cut its long-term rating of Qatar by one notch to AA- from AA and put the rating on CreditWatch with negative implications, meaning there was a significant chance of a further downgrade.
Qatar's Ministry of Defence, meanwhile, played down news reports that its military forces were put on high alert on the country's southern border with Saudi Arabia.
"The Ministry of Defence is always on alert to protect the borders of the state of Qatar from a 360-degree approach - land, sea and air - 24 hours a day, every day of the year," said a ministry statement sent to Al Jazeera.
Source: Al Jazeera and news agencies