US Secretary of State Rex Tillerson has met the king of Saudi Arabia and officials from other countries lined up against Qatar as he works to end a rift that has left the tiny, energy-rich state isolated from its neighbours.
His trip from Kuwait to the western Saudi city of Jiddah follows talks the previous day with the emir of Qatar, Sheikh Tamim bin Hamad Al Thani.
He has also held discussions with the ruler of Kuwait, who is mediating the dispute.
Saudi Arabia, the United Arab Emirates, Egypt and Bahrain severed relations with Qatar and cut air, sea and land routes with it more than a month ago, accusing it of supporting extremist groups.
Qatar denies the allegations.
Mr Tillerson met with Saudi King Salman following his arrival in the Red Sea city and later sat down for talks with foreign ministers from the anti-Qatar quartet.
He will likely press the bloc to ease up on some of its demands after he secured a deal with Qatar on Tuesday to intensify its fight against terrorism and address shortfalls in policing terrorism funding.
The four countries issued a tough 13-point list of demands to Qatar last month that included shutting down its flagship Al-Jazeera network and other news outlets, cutting ties with Islamist groups such as the Muslim Brotherhood, limiting ties with Iran and expelling Turkish troops stationed in the country.
Qatar has rejected the demands, saying that agreeing to them wholesale would undermine its sovereignty.
The head of Qatar's government communication office, Sheikh Saif bin Ahmed Al Thani, accused the quartet on Tuesday of organising "a smear campaign in the international media to damage Qatar's reputation" and said they are "not interested in engaging in honest negotiations to resolve our differences".
The anti-Qatar bloc took partial credit for the US counter-terrorism deal Qatar signed on Tuesday, saying it was the result of "repeated pressures and demands" by them and others, but said it fails to go far enough.
While welcoming US-led efforts to dry up terrorist funding, they maintained a hard line that Qatar must meet their list of what they said were "fair and legitimate demands".
"The quartet affirms that the measures they have taken were motivated by the continuous and diversified activities of the Qatari authorities in supporting, funding and harbouring terrorism and terrorists, as well as promoting hateful and extremist rhetoric and interfering in the internal affairs of states," they said in a joint statement.
The deal struck between Washington and Doha essentially enhances co-operation between the two countries and falls far short of the sweeping demands made by the Arab quartet for Qatar to change its policy of supporting opposition Islamists in the region.
The group has mixed its accusations that Qatar supports extremists with demands that it end support for political dissidents that they have branded as terrorists.
That broad definition of terrorism is seen as an overreach by Western allies, which do not view groups like the Muslim Brotherhood as terrorist organisations.