Allegations that a leading U.S. senator acted secretly to advance Egyptian interests in a bribery scheme have injected a new, combustible element into Washington’s relationship with Cairo, testing a partnership already strained by growing regional competition and friction over human rights.

The Justice Department on Friday announced an explosive indictment against Sen. Robert Menendez - the influential New Jersey Democrat who chairs the Senate Foreign Relations Committee - and his wife in what prosecutors described as a complex cash-for-influence arrangement.

Federal agents cited the discovery of gold bars and over $480,000 in cash hidden in Menendez’s New Jersey home, which they alleged were received from an Egyptian-American business and other associates in exchange for favors, some of which benefited the government of President Abdel Fatah El-Sisi.

Most worrying for the Biden administration may be the array of unnamed Egyptian officials, at least some from Egypt’s military and intelligence services, who prosecutors described seeking information and influence in direct interactions with Menendez and his wife, or via their associates.

The allegations involving a historic foreign partner and one of the country’s most prominent figures on global affairs come at a sensitive moment in Washington’s relations with the Middle East, as the Biden administration seeks to refocus on China and Russia while also bolstering regional security and reassuring partners concerned about an American exit.

Menendez’s committee position gives him special sway over the vast U.S. portfolio of arms sales and assistance to Cairo, including the annual allotment of $1.3 billion in foreign military financing that for decades has made Egypt one of the largest U.S. aid recipients. It was not immediately clear what role, if any, Menendez, who as chairman has the ability to block aid or sales, had in shaping U.S. decisions about arms sales or aid to Egypt.

Steven Cook, a scholar at the Council on Foreign Relations, said U.S. officials’ growing dealings with the Gulf on Middle East issues, along with the Sisi government’s anger about criticism over democracy and human rights, has focused the two countries’ interactions on a narrow set of issues, most notably U.S. aid and Cairo’s ability to broker cease fires in the Gaza strip.

“I don’t see how the indictment will affect the overall bilateral relationship other than sow further mistrust on both sides,” Cook said.

But critics of Egypt’s rights record said the government’s alleged attempt to secure covert influence must be met with a strong response. Seth Binder, an official at the Project on Middle East Democracy, said the charges raised “serious concerns” about Egyptian attempts to interfere in U.S. politics.

He called on Congress to block pending U.S. aid “in order to make crystal clear that al-Sisi’s human rights record and infiltrating the U.S. political system will not be tolerated.”

For the Biden administration, the allegations against a key congressional ally come at uncomfortable moment, as officials seek passage of billions of dollars in new spending for Ukraine. The White House did not immediately respond to questions about the allegations. Secretary of State Antony Blinken, asked in New York about the indictment, cited an “ongoing legal matter” and declined to comment.

The Egyptian government and the Egyptian embassy in Washington did not immediately respond to requests for comment.

Menendez, who was reelected after beating earlier corruption charges, denied any wrongdoing and accused prosecutors of misrepresenting his work in Congress. Under Senate rules, he is required to step down from his position as committee chair.

Among the charges in the indictment is an alleged arrangement in which Menendez promised to facilitate continued aid and arms sales to Cairo in exchange for his wife being put on the payroll of an Egyptian-American businessman, Wael Hana.

In another incident, Menendez allegedly used his clout with the State Department to acquire unclassified but sensitive information about staffing in the U.S. Embassy in Cairo, which was then relayed by his wife to Hana, and then to the Egyptian government. In another instance, Menendez allegedly helped an Egyptian official “ghostwrite” a letter that was intended to be sent to other U.S. senators requesting the release of aid funds.

The indictment comes a week after the Biden administration made a closely watched decision on military aid to Egypt, withholding millions of dollars subject to human rights conditions but authorizing the payment of other such funds.

For Sisi, a former general who took power in a 2013 military coup, securing continued U.S. aid is critical. Egypt is in the throes of a major economic crisis, with record inflation fueling discontent as Sisi prepares to run for reelection in several months. Sisi and the military establishment hold vast sway over politics, governance and the economy - but soaring food prices and a wheat shortage sparked the revolution that toppled the last dictator’s government.

Since President Biden took office in 2021, vowing to put human rights at the center of his foreign policy, Sisi has taken a number of steps to clean up his image. He has pardoned a number of high-profile political prisoners and launched a national dialogue through which actors across the political spectrum, with the exception of Islamists, were invited to debate and propose reforms.

But rights groups say the measures, while welcome, are window dressing on a broader clampdown on government critics. Tens of thousands of “unjustly detained” prisoners remain behind bars, according to Human Rights Watch, and reports of torture abound. Arrests on political grounds have outpaced releases of political prisoners, the Egyptian Commission for Rights and Freedoms, a Cairo-based human rights groups, told The Washington Post this month.

On Saturday, just two days after the State Department decision on military aid, prominent opposition leader Hisham Kassem was sentenced to six months in prison on speech-related charges that rights groups decried as spurious.

While its relative importance in U.S. policy in the Middle East has diminished as the global clout and wealth of Gulf nations has grown, Egypt continues to occupy a key role in U.S. dealings with the region. Egypt’s influence in the Gaza Strip, a top security priority of U.S. ally Israel, remains a key interest, as does its willingness to crack down on Islamists in the Sinai Peninsula.

At times, Washington and Cairo have ended up on different sides of global issues, as in Libya, where Egypt provided years of backing to strongman Khalifa Hifter. The increasing regional influence of Russia and China has heightened the stakes for U.S. diplomats. A massive intelligence leak earlier this year shed new light on those concerns, revealing that Sisi had planned to secretly supply rockets to Russia until U.S. officials stepped in to strong-arm the strongman into supplying arms to Ukraine instead.

Menendez was one of a bipartisan group of lawmakers who met with Sisi during a visit to Egypt in late August. According to statements from Sisi and Sen. Lindsey O. Graham (R-S.C.), who was also part of the delegation, the group discussed topics including negotiations between Sudan, Ethiopia and Egypt over the Grand Ethiopian Renaissance Dam - a massive infrastructure project that Egypt views as a threat - and U.S. efforts to broker ties between Israel and Saudi Arabia.

Menendez has periodically spoken out regarding human and political rights in Egypt, issuing at least 10 tweets about political prisoners or related matters since 2019.

While the alleged bribery scheme involving Menendez may be unprecedented, Mai El-Sadany of the Washington-based Tahrir Institute for Middle East policy noted earlier efforts by the Egyptian government to extend covert influence in the United States. In January 2022, the FBI charged an Egyptian-American man with spying on opponents of Sisi in the United States.

“This is a clear instance of the Egyptian authorities trying to influence our system of governance, and it needs to be part of the conversation,” said El-Sadany.

Michael Birnbaum and John Hudson in New York contributed to this report.