Moscow - Russia Saturday called for dialogue to resolve a dispute between Qatar and its Gulf neighbours, as Riyadh and its allies welcomed US President Donald Trump's demand that Doha stop funding extremist groups.

Rights group Amnesty International warned of "heartbreak and fear" suffered by ordinary people caught in the diplomatic crossfire.

Moscow's appeal came after US Secretary of State Rex Tillerson encouraged Saudi Arabia and its allies to ease their land and sea "blockade" of gas-rich Qatar.

On Monday, Saudi Arabia, Bahrain, Egypt, the United Arab Emirates, Yemen and the Maldives severed ties with Qatar, accusing it of backing terrorism, and imposed punitive measures.

Qatar called the accusations baseless and dispatched Foreign Minister Sheikh Mohammed bin Abdulrahman Al-Thani on a diplomatic offensive to enlist support from abroad. On Saturday he was in Moscow to see Russian Foreign Minister Sergei Lavrov, a day after visiting Germany and Brussels.

"We cannot be happy in a situation when the relations between our partners are worsening," Lavrov said. "We are in favour of resolving any disagreements through... dialogue."

Russia is "ready to try to do everything in its power" to help resolve the crisis, he said.

Sheikh Mohammed said his aim was to inform Russia about "the illegal measures" taken against Qatar. "Differences are always solved by dialogue and the (Gulf) Cooperation Council is the most suitable framework for these talks," he said.

Qatar, Saudi Arabia, the UAE and Bahrain are all in the GCC. Its other two members, Kuwait and Oman, have not severed ties with Doha, and Kuwait has been trying to mediate. But the crisis appeared to escalate on Friday as Saudi Arabia released a joint statement listing 59 Qatari entities and individuals, including members of the royal family, as involved in "terrorist" activities.

German Chancellor Angela Merkel said on Friday she was concerned about the situation in Qatar, adding that all Gulf nations, and also Iran and Turkey, should work together to resolve the regional dispute.

Merkel, who was speaking in Mexico City alongside Mexican President Enrique Pena Nieto, said it would be impossible to sort out the "very unsettling" situation unless all regional actors were involved. She added that it was vital the states of the Gulf Cooperation Council worked together to end the crisis.

"We have to see that the political solution of conflicts ... such as the situation in Syria, such as the situation in Libya or the situation in Iraq, won't happen if certain players are no longer even included in the conversation, and that includes Qatar, it includes Turkey, it includes Iran," she said.

Niger said on Saturday it had recalled its ambassador to Qatar in solidarity with Arab countries that have cut ties with Doha over allegations it sponsors Islamist militants and Iran.

Some African countries have cautiously come out in support of attempts to isolate Qatar.

Mauritania, an Arab League member, cut ties on Tuesday and central African oil producer Gabon condemned Qatar for failing "on counter-terrorism.". Senegal has said it would recall its ambassador in Qatar and expressed its "active solidarity".

Trump told a White House news conference Qatar "has historically been a funder of terrorism at a very high level" and said "they have to end that funding". Qatar's detractors seized on his remarks as vindication of their stance.

The United Arab Emirates welcomed "President Trump's leadership in challenging Qatar's troubling support for extremism". Saudi Arabia called for an immediate change of policy by Qatar.

"Fighting terrorism and extremism is no longer a choice, rather... a commitment requiring decisive and swift action to cut off all funding sources for terrorism regardless of its financier," the Saudi Press Agency cited an official source as saying.

Bahrain also said Qatar needed to "correct its policies" and fight terrorism.

Saudi Arabia and its allies accuse Qatar of sponsoring extremist groups, some allegedly linked to Riyadh's arch-foe Iran, fomenting trouble across the region.

They also resent Doha's ties to the Muslim Brotherhood movement and its sponsorship of the pan-Arab satellite television network Al-Jazeera, which has given opposition figures a platform.

Qatar has denounced the allegations and received backing from its close ally Turkey, whose parliament approved the deployment of troops to defend the emirate.

Turkish President Recep Tayyip Erdogan on Friday said he has never known Qatar to support "terror" organisations and vowed to "continue to give all kinds of support" to Doha.

On Saturday, Erdogan held talks in Istanbul with Bahrain's foreign minister, Turkish media reported.

Trump's Qatar comments Friday overshadowed earlier remarks by Tillerson that the stand-off was hindering the US-led fight against the Islamic State group.

"The blockade is hindering US military actions in the region and the campaign against ISIS," Tillerson warned, referring to the land and sea blockade imposed on Qatar.

But US officials insisted the message was the same - countries in the region should not allow their differences to hamper the fight against extremism.