ROME — The Vatican on Tuesday answered its critics and defended its pursuit of an extended agreement with China on bishop nominations, acknowledging difficulties but insisting the effort had achieved limited, positive results.

The Holy See articulated its position on the eve of a visit by U.S. Secretary of State Mike Pompeo, who this month wrote a harsh critique of the Vatican's 2018 accord with China and suggested the Vatican had compromised its moral authority by signing it. Pompeo is scheduled to headline a religious liberty conference on Wednesday with the Vatican secretary of state and foreign minister, two architects of the deal.

The 2018 accord was aimed at uniting the Catholic flock in China, which is divided between an official church recognized and regulated by the Beijing government, and an underground church that has been loyal to Rome.

The agreement, which included a process for nominating new bishops and regularizing the status of seven bishops who weren't recognized by Rome, was intended as a first step toward thawing decades of estrangement between China and the Vatican.

Critics of the accord, including the retired archbishop of Hong Kong, some underground faithful in China and conservative Catholics elsewhere, accused the Vatican of betraying Catholics in China who for decades refused to join the state-sanctioned church.

The critics say the deal also has emboldened the Beijing government in its harsh crackdown on religious believers that has only increased in the two years since the accord was signed.

Pompeo criticized the accord in an essay published in the conservative ecumenical magazine First Things, echoing the Trump administration's overall criticism of Beijing that has grown amid the coronavirus pandemic in an election year.

"Two years on, it's clear that the Sino-Vatican agreement has not shielded Catholics from the (Communist) Party's depredations, to say nothing of the Party's horrific treatment of Christians, Tibetan Buddhists, Falun Gong devotees and other believers," Pompeo wrote.

Noting that the deal is up for renewal when it expires next month, Pompeo wrote: "Now more than ever, the Chinese people need the Vatican's moral witness and authority in support of China's religious believers."

In its first official response to such criticism, Vatican editorial director Andrea Tornielli recalled that the accord only covers bishop nominations, and did not enter into political or diplomatic relations with China.

"The Provisional Agreement exclusively treats the process for the appointment of bishops: an essential question for the life of the church and for the necessary communion between the pastors of the Chinese Catholic Church with the bishop of Rome and with the bishops throughout the world," Tornielli wrote in an editorial appearing in Wednesday's edition of the Vatican newspaper, L'Osservatore Romano.

Tornielli quoted the Vatican secretary of state, Cardinal Pietro Parolin, as saying it was worth negotiating an extension to the deal despite unspecified "difficulties" aggravated by the virus outbreak.

"Even though contact was blocked in recent months due to the pandemic, the results have been positive, although limited, and suggest going forward with the application of the agreement for another determined period of time," he said.

The issue of bishop nominations had been the main stumbling block to restoring diplomatic relations that were severed nearly seven decades ago when the Chinese communists came to power.

Beijing had long insisted that it must approve appointments as a matter of its national sovereignty; the Vatican has insisted on the pope's divine authority to choose the successors of Christ's apostles.

Details of the 2018 accord never were released. Francis has said it involves a process of dialogue, including over the nomination of bishop candidates, but that he has the final say.

Vatican officials have acknowledged the agreement is far from ideal and represented the best agreement it could get. They said that if the Vatican didn't hammer out something new, there was a risk of the Catholic Church in China becoming irrevocably split.

The Rev. Bernardo Cervellera, a China-watcher and editor of the Catholic news agency AsiaNews, said the accord hadn't borne much fruit in the past two years other than preventing a possible schism if China continued nominating bishops without the pope's consent.

"However, the fact remains that during all this time, there has been an increase in the persecution and control of diverse (religious) communities, both underground and official," he said in an interview.

As evidence, Cervellera cited restrictions forbidding children to attend Mass or receive religious education, as well as reports of even official churches in China coming under televised surveillance.

"It's clear that the Vatican wants this (deal) because it hopes that this little, fragile thing can grow into other aspects of the life of the church," he said.

China, for its part, has defended its treatment of religious groups, including restrictions on minors attending religious services. Recent actions that followed Beijing's long-standing policies on Muslim groups reflect China's increasingly harsh approach toward all ethnic and religious minorities under the Communist Party's leader, President Xi Jinping.

Demands that minority groups adopt national standards in education and culture have been accompanied by well-documented crackdowns on Tibetans, Uighurs and other Xinjiang Muslims, and the destruction of places of worship, including the removal of exterior crosses from church buildings.

The other prong of Xi's crackdown is aimed at giving new life to the atheist party's dedication to the eradication of religion in general.

One of the Vatican accord's biggest critics has been the retired archbishop of Hong Kong, Cardinal Joseph Zen, who has accused Parolin, the secretary of state, of "manipulating" the pope into agreeing to the deal and selling out China's underground faithful in the process.

Zen was in Rome earlier this week, hoping to meet with Francis to discuss developments in China and Hong Kong, Italian media reported. He left without getting an audience.