US spy chief James Clapper will brief senators Wednesday on intelligence issues tied to a landmark nuclear treaty with Russia, amid worries about Moscow's compliance, a lawmaker said Tuesday.

Republicans have concerns about the agreement and "we'll raise those in the closed hearing" said Senator Kit Bond, the top Republican on the Senate Intelligence Committee.

Clapper, the US director of national intelligence, will head to the capitol in the early evening, one Senate aide said on condition of anonymity. Another confirmed that the briefing would occur without specifying a timeframe.

The US Senate is expected to vote on ratifying the new Strategic Arms Reduction Treaty (START) after November elections that are expected to deal a blow to President Barack Obama's Democratic allies in the congress.

The Senate Foreign Relations Committee endorsed the agreement in a 14-4 vote on September 16 even after one of the panel's Republican members, Senator James Risch, said the US intelligence community had shared "troubling" new information with lawmakers.

Lawmakers were tight-lipped about the details at the time, though Bond warned in a statement about "the treaty's lack of verification necessary to detect Russian cheating."

Asked whether there was anything new given longstanding allegations of Russian non-compliance, Risch told reporters after the committee vote: "You haven't seen the same stuff I've seen," but would not elaborate.

The treaty -- signed by Russian President Dmitry Medvedev and Obama at an elaborate ceremony in Prague in April -- restricts each nation to a maximum of 1,550 deployed warheads, a cut of about 30 percent from a limit set in 2002.

The agreement, a top Obama foreign policy initiative, replaces a previous accord that lapsed in December 2009 and also requires ratification by Russia's lower house, the Duma.

US Senate ratification requires 67 votes, Democrats control 59 seats, and just three Republicans on the foreign relations committee voted in favor of the accord, with four against.

Republicans have charged the accord could hamper US missile defense plans -- a charge denied by the Pentagon -- have concerns about Russian implementation, and want assurances about plans to modernize the existing US nuclear arsenal.