*China asks US to stop putting 'maximum pressure' on Iran
*Iran urges friendly countries to buy more Iranian oil
*Britain demands Iran free seized ship, rules out swapping oil tankers
*Second UK warship arrives in the Gulf
Iran said on Monday the US had rejected an offer from Tehran for more robust nuclear inspections in exchange for lifting sanctions because Washington is "not seeking dialogue".
Under the 2015 nuclear deal agreed to by Tehran, Iran must ratify a document, known as the additional protocol, prescribing more intrusive inspections of its nuclear programme eight years after the deal was adopted.
"If the US is really seeking an agreement... Iran can make the additional protocol into law (in 2019) and (the US) at the same time bring a plan to the Congress and lift all illegal sanctions," said foreign ministry spokesman Abbas Mousavi.
"But as we predicted it was rejected by them, because we knew that they are not for talks or an agreement that would yield a proper result," he told a news conference.
According to Mousavi, the proposal was made by Foreign Minister Mohammad Javad Zarif during a visit this month in New York to dismiss the idea of "Iran being against talks... (while) America is for dialogue".
Tehran and Washington have been at loggerheads ever since President Donald Trump unilaterally withdrew the US form the nuclear deal last year and reimposed biting sanctions on Iran.
In the face of US sanctions, Iranian Vice President Eshaq Jahangiri on Monday called on China and other countries friendly with Iran to buy more Iranian oil, the oil ministry news website SHANA reported, as Chinese imports plunged.
"Even though we are aware that friendly countries such as China are facing some restrictions, we expect them to be more active in buying Iranian oil," SHANA quoted Jahangiri as telling visiting senior Chinese diplomat Song Tao.
A report from Beijing said China has urged the United States to stop imposing "maximum pressure" against Iran and avoid creating new obstacles for parties to implement the Joint Comprehensive Plan of Action (JCPOA).
Ensuring the full and effective implementation of the JCPOA is both the requirement of UN Security Council resolutions and the only viable and effective approach to resolve the Iran nuclear issue and deescalate tensions, Chinese Foreign Ministry spokesperson Hua Chunying said at a press briefing when asked to comment on a meeting held in Vienna on Sunday.
At the meeting, the parties reaffirmed their commitment to the JCPOA, sought to resolve the issue of Iran's implementation and reiterated their opposition to the US adoption of unilateral sanctions and long-armed jurisdiction to obstruct other countries' implementation of the JCPOA, according to Hua.
Meanwhile, Britain told Iran on Monday that if it wants to "come out of the dark" it must follow international rules and release a British-flagged oil tanker seized by its forces in the Gulf.
Iranian commandos seized the Stena Impero near the Strait of Hormuz on July 19. That was two weeks after British forces captured an Iranian oil tanker near Gibraltar accused of violating sanctions on Syria.
"If the Iranians want to come out of the dark and be accepted as a responsible member of the intentional community they need to adhere to rules-based system of the international community," Foreign Secretary Dominic Raab told Sky News.
Britain last week started sending a warship to accompany all British-flagged vessels through the Strait of Hormuz.
The Defence Ministry said a second warship, the HMS Duncan, had arrived in the Gulf to support the passage of British-flagged ships through the strait, joining the HMS Montrose.
Britain ruled out swapping seized oil tankers with Iran as a second UK warship arrived in the Gulf to conduct convoys that have irritated Tehran.
New British Foreign Secretary Dominic Raab flatly rejected the idea of the two tankers being exchanged or simultaneously released in a bid to dial back the tensions.
"There is no quid pro quo," Raab told BBC radio.
"This is not about some kind of barter. This is about international law and the rules of the international legal system being upheld," he said.
"That is what we will insist on."
Iranian President Hassan Rouhani had hinted earlier that he was open to a tanker swap.