Russia and Egypt have reached a preliminary deal for Cairo to buy arms worth $3.5 billion from Moscow, Interfax news agency quoted the head of a Russian state arms agency as saying on Wednesday.

Speaking during an arms trade exhibition in South Africa, the head of the Federal Service for Military-Technical Cooperation, Alexander Fomin, did not give further details.

Russia, the world's second-largest arms exporter, has sought to boost its military ties with Egypt after relations between Cairo and its long-standing ally Washington soured, causing some defense cooperation between the two countries to be frozen.

The head of Rosoboronexport, a state body that deals with arms exports, said the value of the agency's order book was high in spite of Western sanctions against Moscow over Ukraine.

"Today our orders portfolio stands at $38.7 billion. This is one of the strongest figures Rosoboronexport has had in recent years," Anatoly Isaykin told a news conference at the same arms expo, according to Interfax.

The United States and European Union have targeted Russia's arms industry as part of sanctions against Moscow for what they call its role in fanning separatist unrest in Ukraine.

They accuse Russia of sending weapons and fighters to reinforce rebels battling Ukrainian government troops -- a charge Moscow has rejected.

Ties between Russian President Vladimir Putin and Egyptian president Abdel-Fattah El-Sisi have been developing since Putin gave his backing to El-Sisi's presidential bid during the Egyptian's visit to Moscow in February.

After he went on to become president, El-Sisi paid his first visit outside the Arab world to Sochi, Russia where both leaders discussed the delivery of billions of dollars in arms and free trade ties.

Cairo hosted Russian foreign minister Sergei Lavrvov and defence minister Sergei Shoigu last year to discuss defence cooperation and strengthen mutual ties that have been inactive since the Soviet era—a visit billed by both sides as historic.

Moscow's Vedemosti business daily reported at the time that both sides were nearing a deal on LE21 billion ($3 billion) in missiles and warplanes to Egypt that could be financed by Saudi Arabia and the United Arab Emirates.

Egypt had strong ties with Russia in the 1950s and 1960s, and the Soviet Union was the main supplier of arms to Egypt until the early 1970s. Relations soured after Israel and Egypt signed a peace treaty bringing in some LE9.1 billion ($1.3 billion) in annual US military aid to Cairo in 1979.

Russia provides Egypt's tourism industry – significantly hammered by three years of political turmoil since the 2011 uprising – with over 40 percent of its European tourists.

Cairo and Washington had stressed that mutual ties between the two remain strong despite the North African country drawing closer to its old defence ally.