US Secretary of State Rex Tillerson urged the four Arab countries to lift a land blockade on Qatar considering the tiny Gulf country's latest "positive movement" on counterterrorism.

The Qataris have continued to move forward and have been "very aggressive" in implementing the agreement, Tillerson told reporters Friday before his meeting with visiting Omani Foreign Minister Yusuf bin Alawi bin Abdullah in Washington.

He also said that Qatar has indicated "a willingness" to sit with the four countries and "discuss the demands", Xinhua news agency reported.

Tillerson urged the four Arab parties to begin to take positive action and lift the land blockade as "a sign of good faith".

Last month, Saudi Arabia, the United Arab Emirates, Egypt and Bahrain, cut diplomatic ties and imposed sanctions on their neighbour, accusing it of supporting extremism and terrorism, an allegation denied by Qatar.

The incident has spiralled into one of the worst regional disputes in years.

Last week, Tillerson travelled to the Middle East. During his trip he signed an agreement with Qatar on combating terrorism financing in an effort to ease the tension in the region.

On June 23, the four countries issued a list of 13 demands to end the rift with Doha, including closing Al-Jazeera television and cutting Qatar-Iran diplomatic ties.

Since Qatar's response seemed unsatisfactory, the Arab quartet have decided to maintain their sanctions against Qatar.

Earlier this week, the four seemed to have modified their demands, urging the Gulf nation to commit to six principles on combating extremism and terrorism and negotiate a plan with specific measures to implement them.