Iran and China are expected to sign a controversial 25-year bilateral deal on March 27.

The final details of the agreement have not been disclosed, but it is expected to include Chinese investments in Iran’s energy and infrastructure sectors.

China is Iran’s top trading partner and a key market for Iranian crude exports, which have been severely curtailed by U.S. sanctions.

Iranian Foreign Ministry spokesperson Said Khatibzadeh said on March 27 that the pact includes “political, strategic, and economic” components.

Khatibzadeh said the deal will be signed by visiting Chinese Foreign Minister Wang Yi, who arrived in Tehran late on March 26.

Iranian officials have said that the pact was proposed in a January 2016 trip to Iran by Chinese President Xi Jinping.

Iranians have accused officials of hiding details of the prospective deal amid fears that Tehran may give too much away to Beijing.

Iran has in recent years increasingly reached out to China in the face of growing U.S. pressure to isolate Tehran.

The United States unilaterally pulled out of a 2015 nuclear deal between Tehran and world powers in 2018 under former President Donald Trump.

Trump pursued a policy of “maximum pressure” on Tehran over its nuclear and missile programs, as well as its support for regional proxies.

The deal was meant to provide relief for Iran from international sanctions in exchange for limitations on its nuclear program, which Iran says is strictly for civilian energy purposes.

U.S. President Joe Biden has signaled his readiness to revive the deal.

Based on reporting by Reuters and AFP